During the day, Billy works as tech support at amazon.ca, but at night he runs a fantasy world where he is god. He is the Gamemaster, he creates a fantasy world where he can be anything, do anything, and his only limit is his own imagination. But Billy is better than other roleplaying game nerds, Billy uses his computer skills to turn his fantasy into reality. He programmed his only specialty d20 to bring his fantasy into the real world. Sure his world takes on an 8bit appearance, but he is working on upgrading to 16bit.
Billy met Ramona during her time at amazon.ca. He never actually dated her, but in his fantasy world he was a valiant knight and rescued his dear Princess Ramona. Billy would like nothing more to turn that fantasy into reality.
In battle, Billy uses his d20 to summon orcs, goblins, and other monsters. Sure, Scott Pilgrim can punch the goblins, but if the Gamemaster says there's an army on the other side of the door, Scott will have to defeat them all to keep Ramona. And if Scott manages to defeat them or if Billy rolls a 1, Billy will fight Scott with his fantasy sword powered by the technology of his d20 prototype.
Billy sees the other evil exes as adventurers all trying to find the ultimate treasure, Ramona's heart. And he vows to not fail where his comrades have fallen.
He's like a video game developer and he'll program Scott's game of life for failure.