If Otto is too easy an opponent, try adding some of these additional challenges:

HEAD START: Otto plays two additional cards during setup.

NO JACKBOT: When Otto plays two cards on his turn, do not activate a Starter.

GO BIG: Otto uses the more expensive card each turn, rather than the cheaper.

QUICK TURNAROUND: When Otto plays a Gear card, he immediately takes 1 coin from it.

AN EVEN WILDER OTTO: Set up the game using the An Even Wilder Venture variant. As Otto does not have a personal deck, he will start using the main deck immediately (even during setup!). If Otto runs out of Villager and Gear cards to play during setup, he will Tuck the Building with the highest cost.