Hi! I love this experimental snapshot, you did a great job!

I was testing the combat with Warden and I got it stucked in Sauna structure in the water. It was pretty easy to kill him that way. Maybe if he had higher knockback resistance or path finding around, it could be more challenging. (He got out eventually, (since I was struggling to capture it at first), but he has taken a lot of hit off screen.

Also I got him walking through {}(not falling on) the (naturally generated) dripstone big and small ones and he was taking damage. I think thats odd, because he is literally spawning (or digging up) from the stone itself and can walk around them without taking damage. It may be caused by wall suffocation in the dripstone or something because it happend only few times.
Replication: Find dripstone, spawn Warden a put a bat to trigger him.

Warden can take hits from Wither, but he cannot hit him.

Also known issue:
{}1. Sniff animation in background of ESC menu.
2. Wither/iron golem bug  MC60792 Still in this snapshot

Hope this helps.