Znt

I can confirm this is a Zombie problem.

Check out these Timings from spigot...

I typed /timings on, and then hit /butcher before spawning 150 entities of one type, then /butcher, then another 150 of another type, etc... These are the results:

http://aikar.co/timings.php?url=5876186
Vio Event
21.64% ** tickEntity - EntityZombie
0.08% ** tickEntity - EntitySkeleton
0.08% ** tickEntity - EntityEnderman
0.08% ** tickEntity - EntityPigZombie
0.21% ** tickEntity - EntityCaveSpider