Oh? Sweet. Doesn't seem too complicated in 5E, a little more with stuff like restrained vs prone but it's negligible at a glance.

Does it let dolphins grapple? I'm now totally sold on this character concept lmao. 5E grapple druid is actually pretty workable, strangely, especially at higher level with the better beasties. Does seem a bit weird that something like a mammoth can easily knock things prone but not grapple (even by sitting on them or something), by RAW though. Seems to be mostly if the DM is on board with your character design really or not lol.