Poisonous Zombies!

Zombies that poison you depending on range:

/execute @e[type=Zombie] ~ ~ ~ effect @a[r=4] 19 1 1
/execute @e[type=Zombie] ~ ~ ~ effect @a[r=3] 19 1 2
/execute @e[type=Zombie] ~ ~ ~ effect @a[r=2] 19 1 3
/execute @e[type=Zombie] ~ ~ ~ effect @a[r=1] 19 1 4

Put all of them in a rapid command block clock (that powers all 4)