Thanks for this detailed feedback, it's my favorite kind! Firstly, we're glad you liked the art. And now that you mention it, some squash and stretch really would have helped make things less static, so I'll note that.
And I'm so glad the invincibility mode kept you from giving up, that's why I made it. I've been paranoid about making a game too hard ever since Xanderjam 4, where nobody could finish my game. Thanks to you I can now officially say it's not paranoia, it's practicality.
As far as telegraphing attacks, the mammoth definitely needed it. In fact that's why the T-Rex telegraphs it's next attack by peering over where it'll later bite down at, although some more there wouldn't have hurt. I just never went back and fixed the mammoth. I completely agree that the battles needed more feedback.
At any rate, thanks again for such great suggestions, and thanks for playing!