Drevax, Redstone Enigma

Vigilance.
{1}{u}{u}{u}: Merge target artifact on top of target
other artifact. Then, draw a card for each merged
card you control. ( To merge an artifact, chose a
artifact on the battlefield, then put it on top of
another target artifact. The artifact on top has the
combined mana cost of both artifacts and has all
abilities of the artifacts under it.)