Did I break the game or do I not understand the rules?

I built a Mr Fox deck and in my playtesting I can pretty easily win in one turn. 0 cost cards are incredibly overpowered and it's quite trivial to draw through your whole deck.

My deck is entirely 0 cost cards, which means that I can easily draw 4 cards at the start of my turn. 16ish cards draw at least 1 card, with cards like cuteness overload (destroy creatures and draw for each creature destroyed) allowing for up to 7 cards drawn thanks to holographic rabbit.

My current win condition uses multiple copies of Platypus (+1 att for each unique 0 cost card in my discard) and singing sword (+1 att / 2 cards drawn) to cash out. Tandem bike ensures there are enough open lanes.

If I go second I can win on my first turn quite easily, even if my opponent manages to fill all 4 lanes.

I've barely optimized this deck and it's already absurd. Please tell me I'm missing something in the rules that makes it not as strong as I fear.