diff --git a/bambi/interpret/effects.py b/bambi/interpret/effects.py
index f24b02735..d268c169e 100644
--- a/bambi/interpret/effects.py
+++ b/bambi/interpret/effects.py
@@ -19,10 +19,8 @@
     merge,
     VariableInfo,
 )
-from bambi.utils import get_aliased_name, listify
+from bambi.utils import get_aliased_name
 
-# TODO: aliases for type hints?
-# TODO: functions for error handling
 
 SUPPORTED_SLOPES = ("dydx", "eyex")
 SUPPORTED_COMPARISONS = {
@@ -415,7 +413,7 @@ def average_by(self, variable: Union[bool, str]) -> pd.DataFrame:
             A dataframe containing the marginal or group by average.
         """
         if variable is True:
-            contrast_df_avg = average_over(self.summary_df, None)
+            contrast_df_avg = average_over(self.summary_df, "all")
             contrast_df_avg.insert(0, "term", self.variable.name)
             contrast_df_avg.insert(1, "estimate_type", self.estimate_name)
             if self.kind != "slopes" and len(self.variable.values) < 3:
@@ -433,7 +431,7 @@ def average_by(self, variable: Union[bool, str]) -> pd.DataFrame:
 def predictions(
     model: Model,
     idata: az.InferenceData,
-    conditional: Union[str, list, None] = None,
+    conditional: Union[str, dict, list, None] = None,
     average_by: Union[str, list, bool, None] = None,
     target: str = "mean",
     pps: bool = False,
@@ -451,8 +449,9 @@ def predictions(
     idata : arviz.InferenceData
         The InferenceData object that contains the samples from the posterior distribution of
         the model.
-    conditional : str, list, optional
-        The covariates we would like to condition on.
+    conditional : str, list, dict, optional
+        The covariates we would like to condition on. If dict, keys are the covariate names and
+        values are the values to condition on.
     average_by: str, list, bool, optional
         The covariates we would like to average by. The passed covariate(s) will marginalize
         over the other covariates in the model. If True, it averages over all covariates
@@ -484,15 +483,21 @@ def predictions(
     ------
     ValueError
         If ``pps`` is ``True`` and ``target`` is not ``"mean"``.
+        If ``conditional`` is a list and the length is greater than 3.
+        If ``prob`` is not > 0 and < 1.
     """
-
     if pps and target != "mean":
         raise ValueError("When passing 'pps=True', target must be 'mean'")
 
-    # TODO: error handling
+    if isinstance(conditional, list):
+        if len(conditional) > 3:
+            raise ValueError(
+                f"Only 3 covariates can be passed to 'conditional'. {len(conditional)} "
+                "were passed. If you would like to pass more than 3 covariates, use "
+                "a dictionary."
+            )
 
     conditional_info = ConditionalInfo(model, conditional)
-
     transforms = transforms if transforms is not None else {}
 
     if prob is None:
@@ -500,7 +505,7 @@ def predictions(
     if not 0 < prob < 1:
         raise ValueError(f"'prob' must be greater than 0 and smaller than 1. It is {prob}.")
 
-    cap_data = create_predictions_data(conditional_info, model)
+    cap_data = create_predictions_data(conditional_info, conditional_info.user_passed)
 
     if target != "mean":
         component = model.components[target]
@@ -521,13 +526,13 @@ def predictions(
         idata = model.predict(
             idata, data=cap_data, sample_new_groups=sample_new_groups, inplace=False, kind="pps"
         )
-        y_hat = response_transform(idata.posterior_predictive[response.name])
+        y_hat = response_transform(idata["posterior_predictive"][response.name])
         y_hat_mean = y_hat.mean(("chain", "draw"))
     else:
         idata = model.predict(
             idata, data=cap_data, sample_new_groups=sample_new_groups, inplace=False
         )
-        y_hat = response_transform(idata.posterior[response.name_target])
+        y_hat = response_transform(idata["posterior"][response.name_target])
         y_hat_mean = y_hat.mean(("chain", "draw"))
 
     if use_hdi and pps:
@@ -543,6 +548,7 @@ def predictions(
     upper_bound = 1 - lower_bound
     response.lower_bound, response.upper_bound = lower_bound, upper_bound
 
+    cap_data = cap_data.copy()
     if y_hat_mean.ndim > 1:
         cap_data = merge(y_hat_mean, y_hat_bounds, cap_data)
         cap_data = cap_data.rename(
@@ -559,6 +565,8 @@ def predictions(
         cap_data[response.upper_bound_name] = y_hat_bounds[1]
 
     if average_by is not None:
+        if average_by is True:
+            average_by = "all"
         cap_data = average_over(cap_data, covariate=average_by)
 
     return cap_data
@@ -587,8 +595,9 @@ def comparisons(
         the model.
     contrast : str, dict
         The predictor name whose contrast we would like to compare.
-    conditional : str, dict, list
-        The covariates we would like to condition on.
+    conditional : str, list, dict, optional
+        The covariates we would like to condition on. If dict, keys are the covariate names and
+        values are the values to condition on.
     average_by: str, list, bool, optional
         The covariates we would like to average by. The passed covariate(s) will marginalize
         over the other covariates in the model. If True, it averages over all covariates
@@ -620,10 +629,10 @@ def comparisons(
         If `wrt` is a dict and length of ``contrast`` is greater than 2 and
         ``conditional`` is ``None``.
         If ``conditional`` is None and ``contrast`` is categorical with > 2 values.
+        If ``conditional`` is a list and the length is greater than 3.
         If ``comparison_type`` is not 'diff' or 'ratio'.
         If ``prob`` is not > 0 and < 1.
     """
-
     contrast_name = contrast
     if isinstance(contrast, dict):
         if len(contrast) > 1:
@@ -637,6 +646,14 @@ def comparisons(
                 f"{contrast_name} was passed {len(contrast_values)} values."
             )
 
+    if isinstance(conditional, list):
+        if len(conditional) > 3:
+            raise ValueError(
+                f"Only 3 covariates can be passed to 'conditional'. {len(conditional)} "
+                "were passed. If you would like to pass more than 3 covariates, "
+                "use a dictionary."
+            )
+
     if conditional is None:
         if is_categorical_dtype(model.data[contrast_name]) or is_string_dtype(
             model.data[contrast_name]
@@ -728,8 +745,9 @@ def slopes(
         the model.
     wrt : str, dict
         The slope of the regression with respect to (wrt) this predictor will be computed.
-    conditional : str, dict, list
-        The covariates we would like to condition on.
+    conditional : str, list, dict, optional
+        The covariates we would like to condition on. If dict, keys are the covariate names and
+        values are the values to condition on.
     average_by: str, list, bool, optional
         The covariates we would like to average by. The passed covariate(s) will marginalize
         over the other covariates in the model. If True, it averages over all covariates
@@ -771,6 +789,7 @@ def slopes(
         If length of ``wrt`` is greater than 1.
         If ``conditional`` is ``None`` and ``wrt`` is passed more than 2 values.
         If ``conditional`` is ``None`` and default ``wrt`` has more than 2 unique values.
+        If ``conditional`` is a list and the length is greater than 3.
         If ``slope`` is not 'dydx', 'dyex', 'eyex', or 'eydx'.
         If ``prob`` is not > 0 and < 1.
     """
@@ -787,6 +806,14 @@ def slopes(
                 f"{wrt_name} was passed {len(wrt_values)} values."
             )
 
+    if isinstance(conditional, list):
+        if len(conditional) > 3:
+            raise ValueError(
+                f"Only 3 covariates can be passed to 'conditional'. {len(conditional)} "
+                " were passed. If you would like to pass more than 3 covariates, "
+                "use a dictionary."
+            )
+
     if not isinstance(wrt, dict) and conditional is None:
         if is_categorical_dtype(model.data[wrt_name]) or is_string_dtype(model.data[wrt_name]):
             num_levels = len(model.data[wrt_name].unique())
diff --git a/bambi/interpret/plotting.py b/bambi/interpret/plotting.py
index 3f0429b21..330c77d70 100644
--- a/bambi/interpret/plotting.py
+++ b/bambi/interpret/plotting.py
@@ -13,9 +13,6 @@
 from bambi.interpret.utils import get_covariates, ConditionalInfo
 from bambi.utils import get_aliased_name, listify
 
-# TODO: aliases for type hints?
-# TODO: functions for error handling
-
 
 def _plot_differences(
     model: Model,
@@ -31,7 +28,6 @@ def _plot_differences(
     """
     Common function used for both 'plot_comparisons' and 'plot_slopes'.
     """
-
     if (subplot_kwargs and not average_by) or (subplot_kwargs and average_by):
         for key, value in subplot_kwargs.items():
             conditional_info.covariates.update({key: value})
@@ -87,7 +83,7 @@ def _plot_differences(
 def plot_predictions(
     model: Model,
     idata: az.InferenceData,
-    conditional: Union[str, list, None] = None,
+    conditional: Union[str, list, dict, None] = None,
     average_by: Union[str, list, None] = None,
     target: str = "mean",
     sample_new_groups: bool = False,
@@ -109,8 +105,9 @@ def plot_predictions(
     idata : arviz.InferenceData
         The InferenceData object that contains the samples from the posterior distribution of
         the model.
-    conditional : str, list, optional
-        A sequence of between one and three names of variables in the model.
+    conditional : str, list, dict, optional
+        The covariates we would like to condition on. If dict, keys are the covariate names and
+        values are the values to condition on.
     average_by: str, list, bool, optional
         The covariates we would like to average by. The passed covariate(s) will marginalize
         over the other covariates in the model. If True, it averages over all covariates
@@ -154,30 +151,31 @@ def plot_predictions(
     Raises
     ------
     ValueError
-        If number of values passed with ``conditional`` is >= 2 and
-        ``average_by`` are both ``None``.
         If ``conditional`` and ``average_by`` are both ``None``.
         If length of ``conditional`` is greater than 3 and ``average_by`` is ``None``.
+        If main covariate is not numeric or categoric.
     """
-
     if conditional is None and average_by is None:
         raise ValueError("Must specify at least one of 'conditional' or 'average_by'.")
 
     if isinstance(conditional, dict):
-        conditional = {key: sorted(listify(value)) for key, value in conditional.items()}
-    elif conditional is not None:
+        conditional = {
+            key: np.array(sorted(listify(value))).flatten() for key, value in conditional.items()
+        }
+    elif isinstance(conditional, str):
         conditional = listify(conditional)
-        if len(conditional) > 3 and average_by is None:
-            raise ValueError(
-                "Must specify a covariate to 'average_by' when number of covariates"
-                "passed to 'conditional' is greater than 3."
-            )
+
+    if conditional is not None and len(conditional) > 3 and average_by is None:
+        raise ValueError(
+            "Must specify a covariate to 'average_by' when number of covariates "
+            "passed to 'conditional' is greater than 3."
+        )
 
     if average_by is True:
         raise ValueError(
             "Plotting when 'average_by = True' is not possible as 'True' marginalizes "
-            "over all covariates resulting in a single comparison estimate. "
-            "Please specify a covariate(s) to 'average_by'."
+            "over all covariates resulting in a single prediction estimate. "
+            "Please pass a covariate(s) to 'average_by'."
         )
 
     cap_data = predictions(
@@ -194,6 +192,7 @@ def plot_predictions(
     )
 
     conditional_info = ConditionalInfo(model, conditional)
+    transforms = transforms if transforms is not None else {}
 
     if (subplot_kwargs and not average_by) or (subplot_kwargs and average_by):
         for key, value in subplot_kwargs.items():
@@ -267,7 +266,8 @@ def plot_comparisons(
     contrast : str, dict, list
         The predictor name whose contrast we would like to compare.
     conditional : str, dict, list
-        The covariates we would like to condition on.
+        The covariates we would like to condition on. If dict, keys are the covariate names and
+        values are the values to condition on.
     average_by: str, list, optional
         The covariates we would like to average by. The passed covariate(s) will marginalize
         over the other covariates in the model. Defaults to ``None``.
@@ -306,11 +306,11 @@ def plot_comparisons(
     Raises
     ------
     ValueError
+        If the number of contrast levels is greater than 2 and ``average_by`` is ``None``.
         If ``conditional`` and ``average_by`` are both ``None``.
         If length of ``conditional`` is greater than 3 and ``average_by`` is ``None``.
-
-    Warning
-        If length of ``contrast`` is greater than 2.
+        If ``average_by`` is ``True``.
+        If main covariate is not numeric or categoric.
     """
     contrast_name = contrast
     if isinstance(contrast, dict):
@@ -350,8 +350,8 @@ def plot_comparisons(
     if average_by is True:
         raise ValueError(
             "Plotting when 'average_by = True' is not possible as 'True' marginalizes "
-            "over all covariates resulting in a single comparison estimate. "
-            "Please specify a covariate(s) to 'average_by'."
+            "over all covariates resulting in a single prediction estimate. "
+            "Please pass a covariate(s) to 'average_by'."
         )
 
     conditional_info = ConditionalInfo(model, conditional)
@@ -413,7 +413,8 @@ def plot_slopes(
         If 'wrt' is numeric, the derivative is computed, else if string or categorical,
         'comparisons' is called to compute difference in group means.
     conditional : str, dict, list
-        The covariates we would like to condition on.
+        The covariates we would like to condition on. If dict, keys are the covariate names and
+        values are the values to condition on.
     average_by: str, list, bool, optional
         The covariates we would like to average by. The passed covariate(s) will marginalize
         over the other covariates in the model. If True, it averages over all covariates
@@ -464,11 +465,12 @@ def plot_slopes(
     Raises
     ------
     ValueError
-        If number of values passed with ``conditional`` is >= 2 and
-        ``average_by`` are both ``None``.
+        If the number of ``wrt`` values is greater than 2 and ``average_by`` is ``None``.
         If ``conditional`` and ``average_by`` are both ``None``.
         If length of ``conditional`` is greater than 3 and ``average_by`` is ``None``.
+        If ``average_by`` is ``True``.
         If ``slope`` is not one of ('dydx', 'dyex', 'eyex', 'eydx').
+        If main covariate is not numeric or categoric.
     """
     wrt_name = wrt
     if isinstance(wrt, dict):
@@ -508,8 +510,8 @@ def plot_slopes(
     if average_by is True:
         raise ValueError(
             "Plotting when 'average_by = True' is not possible as 'True' marginalizes "
-            "over all covariates resulting in a single slope estimate. "
-            "Please specify a covariate(s) to 'average_by'."
+            "over all covariates resulting in a single prediction estimate. "
+            "Please pass a covariate(s) to 'average_by'."
         )
 
     if slope not in ("dydx", "dyex", "eyex", "eydx"):
diff --git a/bambi/interpret/utils.py b/bambi/interpret/utils.py
index f2208e4e4..7409a79f5 100644
--- a/bambi/interpret/utils.py
+++ b/bambi/interpret/utils.py
@@ -180,12 +180,12 @@ class Covariates:
     panel: Union[str, None]
 
 
-def average_over(data: pd.DataFrame, covariate: Union[str, list, None]) -> pd.DataFrame:
+def average_over(data: pd.DataFrame, covariate: Union[str, list]) -> pd.DataFrame:
     """
     Average estimates by specified covariate in the model. data.columns[-3:] are
     the columns: 'estimate', 'lower', and 'upper'.
     """
-    if covariate is None:
+    if covariate == "all":
         return pd.DataFrame(data[data.columns[-3:]].mean()).T
     else:
         return data.groupby(covariate, as_index=False)[data.columns[-3:]].mean()
@@ -359,6 +359,7 @@ def set_default_values(model: Model, data_dict: dict, kind: str) -> dict:
             if not isinstance(value, (list, np.ndarray)):
                 data_dict[key] = [value]
         return data_dict
+
     return data_dict