Andromeda Eldoris

Hexproof.
First strike.
Double strike.
{u}{3}:Gain control of target artifact.
At the beginning of your upkeep if you control 3
or more artifacts, exile Andromeda Eldoris, then
return her to the battlefield transformed under
her owner's control. If you do, Search your
library for a card called The Realm Walker
and put it on the battlefield.