Wandering Shell-Walker

{1}{u}{r}: You may have Wandering Shell-Walker become a Cauldron until the end of turn, it loses all other abilities and gains. While Wandering Shell-Walker is a Cauldron, other Machine gains convoke. (Your creature can help cast that spell.
Each creature you tap while casting that spell pays {1}
or one mana of that creature's color.)

Whenever another Machine enters the battlefield under you control, put a +1/+1 counter on Wandering Shell-Walker.