All mobs have half their health. It takes 10 hits from a fist to kill Creepers, Skeletons, Zombies. 8 to kill Spiders, Big Slimes, and Villagers. 6 to kill Cave Spiders. 5 to kill Ghasts, Cows, Pigs. 3 to kill Bats, 2 to kill Small Slimes, Chickens. 1 to kill Baby Slimes as usual though.