/summon WitherBoss ~ ~1 ~ {NoAI:1b,Invulnerable:1b,CustomName:"boss name",Silent:1b,Health:1}
The summoned wither will have 1 health, and can be punched to death, has the wither armor, but shows full health.
/entitydata @e[type=WitherBoss] {NoAI:0}
do this, and the health will drop down quickly.
really annoying as I and my friend play together and everything breaks randomly.