Re-add the giant AI in minecraft 1.9 with these commands! by char

Put /tp @e[type=Giant] @e[type=Zombie,name=Giant] in a repeat always active command block.

Then, /summon Zombie ~0 ~1 ~0 {ArmorItems:[{},{},{},{id:chainmail_helmet,tag:{Unbreakable:1}}],CustomName:Giant,CustomNameVisible:1,Attributes:[{Name:generic.movementSpeed,Base:0.1},{Name:generic.attackDamage,Base:50}],ActiveEffects:[{Id:14,Amplifier:1,Duration:999999},{Id:10,Amplifier:1,Duration:999999}],Glowing:1,PersistenceRequired:1,Health:500.0f}

Next, /summon Giant ~0 ~1 ~0 {PersistenceRequired:1}