Killing a critter (Pokeshell Spawn) while they are being wrangled makes them be listed as dead while still being alive.
1. Wrangle a Pokeshell Spawn.
2. While they are being wrangled, kill them. (But don't tell the critter I made you do it.)
(In the included picture I had issued a new attack command. The attack command in the pick isn't part of the bug report.)
The critter animation continues even with its health bar at zero.
It seems to just be an "empty" animation. It stays in the same spot, floating in the air if you remove tiles underneath it. The pic below is the same Pokeshell Spawn, with the base evolving around/on top of it.