This appears related to the fix you made for V1.29
Using Polymorphism with Wild Shape doesn't seem to be calculating skills and saves correctly based on my understanding. The feature says:
Per Jeremy Crawford on Twitter (
https://twitter.com/JeremyECrawford/...55703530672128) Referring to the proficiency bonus in the stat block since many beasts will have a lower proficiency bonus than the druid would at the level the druid gains the ability to wild shape into the beast.
My understanding is that the calculation for any physical skill or save starts with the beast's ability score and then gets the druid's or beast's proficiency added to it. Similarly, any mental skill or save starts with the druid's ability scores and then adds either the beast's or druid's proficiency. I made a test druid to show what I'm talking about. (see attachment)
Attachment 53868 The druid has 20 in all ability scores and shifts into a Giant Hyena that only has 16 Strength, 14 Dexterity, and 14 Constitution. The physical saves should just use the Giant Hyena's ability bonus, but it is pulling from the druid's ability bonuses. Also the Giant Hyena has proficiency in Perception while the druid doesn't so it should be using the druid's Wisdom bonus and adding the Giant Hyena's proficiency bonus.
The extension appears to be taking the higher total bonus for saves using whichever form's bonus is higher. It also doesn't seem to be modifying skills based on the baseline ability score. If a form has proficiency in a skill that the other doesn't, it is just taking that form's skill modifier.
Unless of course my understanding of the RAW is wrong and the extension calculations are following the RAW.