Cadaver Bear is a Zombie variant of Teacher Bear. It burrows under cats, moves significantly faster, gets knocked back only four times and attacks non-stop like Assassin Bear, allowing it to push much more easily than Teacher Bear. Unlike most other Zombies, it revives with 100% HP instead of 50%.
It's recommended to stall this enemy with tons of preferably strong meatshields. DO NOT USE ANY ATTACKERS WITH UNDER 360 RANGE, as they will be killed nearly instantly by its non-stop attack rate. Therefore, the only anti-Zombie Rare Cats that can outrange this monster are Corrupted Psychocat and Cataur (365 and 390 respectively), with Target Zombie Talents. Although Corruputed Psychocat has been well-known to be a reliable support unit, he mostly fails to slow down Cadaver Bear due to his speed and short range differences. Cataur, however, can be a very potent attacker, especially with the Zombie Killer Talent unlocked.
Eternal Reika and all Uber Rares from the Iron Legion event are exceptional counters to this enemy, as long as they're protected by meatshields. As much as possible, DO NOT LET IT REVIVE UNDER ANY CIRCUMSTANCES. Best case scenario, he revives at his base. Worst case scenario, it revives in front of your attackers and quickly demolishes them.