`FindCheapestActionToCombineWith` I think a name like that would make this clearer as to what this does.

```suggestion /// Finds the way to combine an action with previous actions so that the maximum amount of MP is saved. ```

I'm a bit suspicious about the cast here. What guarantees this doesn't fail?

```suggestion /// <param name="previousData">A list of data <see cref="currentData"/> may combine with</param> ```

```suggestion // If mode is the following, no more checks are needed. ```

```suggestion GetLeastCostCombinedTuple(EditorCombinableActionData currentData, ```