Biovisionary+Kiki Jiki, Mirror Breaker+Intruder Alarm

Auto win on the fifth turn

Conspiracy+Rooftop Storm

All your creatures cost 0.

Living Plane+Electrickery

Destroy your opponents lands for six mana

Grimgrin, Corpse-Born+Elemental Mastery

Infinite power and creatures.

Necrotic Ooze+Palladium Myr and Pili-Pala in the graveyard

Infinite mana of any color

Mycosynth Lattice+Darksteel Forge+Nevinyrral's Disk

Quite a bit of mana but let's you repeatedly wipe the opponents board (for one mana) will leaving your stuff alone.

Quillspike+Devoted Druid+Rites of Consumption

Repeatedly tap devoted Druid, place a -1/-1 counter on it, then eat that counter with quill spike and the mana you created. When Quillspike is big enough, play Rite of Consumption to kill an opponent.