MTG Salvation

So, uh. If i get that right, playing this while controlling a changeling is essentially WW.

Unless something like Sphere of Resistance is in play, yes.

Turn 1 Mothdust/Outcast into this on turn 2 seems like a beating and a half. Outside of those, there's a grand total of eleven one-drop creatures legal in Modern that can reduce this guy's cost by 3 — and none, I should be quick to note, share a creature type with either Memnite or Ornithopter, if you want to go full gimmick mode.

This doesn’t say “other” so it should count itself as changeling as it stands... should be errataed.
I stand corrected. Please see post below explaining my folly.

As a spell, the card does not count as "a creature you control" meaning it would not reduce it's own casting cost.

Wait... So the changeling is now a horse AND a rider?

Not the first time.