Tying wildshape to level/4 in CR?

[AdamBank]

Are there any inherent problems with basing wildshape (or a similar shapechanging ability) on the desired shape's CR? For example, at fourth level, a druid can wildshape into any animal with a CR of 1 or lower. The possible CR of the wildshape increases by 1 every 4 full levels (plus you get to pick other creature types to shift into). I know Challenge Ratings aren't the most analytically sound measurement in the world, but it seems like an intuitive way to link the power level of shapeshifter to the level of the shapeshifter.

(In historical Celtic poetry, Taliesin the bard was a powerful wildshaper. I have often thought of swapping out the bard's song ability for a wimpy version of wildshape, and I was wondering if this would do the trick).

 

[Terath Ninir]

While your idea isn't bad in concept, it has a few execution problems.

1) You have to trust the people who make up the CRs. I don't, to a good degree. I accidentally almost got a Total Party Kill once because I selected a demon by CR without first looking through the whole description.

2) Your ability is too weak. CR 1 is fine at 4th level. But CR 2 at 8th level? Wolverines and boar forms are just not going to help that much at that level. One CR every two levels (6th, 8th, 10th, etc.) might work a little better, but you'd have to look at the animals of each CR to make sure.

(3. Well, they still don't have very good guidelines for making customized classes, but switching bardic music for wildshape would seem like a reasonable trade. Wildshape is more powerful, but doesn't come in until 4th level. And bardic music, at least at first glance, seems better in 3.5, so that helps make it more of a fair trade.)