I wasn't doing too hot in the beginning, playing as isaac, I randomly picked up an item that doubled my spiders/fly size, even though I didn't have spiders or flies. Then, I picked up Fly love after a few other items and became Lord of The Flies, and holy shit is that awesome. It turns all enemy flies into your flies, and they attack whatever. Then, I went hard on Guppy items, and became Guppy with double sized flies, afterwards I went and beat Satan for the first time. So OP.