An OTK that actually wins half the time
The surprising thing about this deck is that it actually wins as often as it loses (which isn't something I'd expect an OTK deck to do).
The combo takes 13-18 Faeria.
0. Setup: Survive using typical BG Swarm. Use Curious Biomancer to draw 3 Spirit of Rebirth and the Barrensky Vermin. Get enough lands on board. Play all creatures from your hand except the Spirit of Rebirths and Barrensky Vermin.
1. Play 2-3 Spirit of Rebirth and a Rain of Fish.
2. Wait for your creatures to die, buffing the Barrensky. (Or, if you have Famine, you can play it for a quick +18/+18 or more.)
3. Play the Barrensky and imagine your opponent's jaw dropping.
It's essentially a two-card combo: Curious Biomancer and Rain of Fish, because the Biomancer can reliably draw the other four cards.
And hey, if that doesn't work, you can always fall back to the standard Rain+Gift and hit them in the face.