Play permanents, typically you want 8 mana up at the end of their turn, return 5+ permanents, fateful showdown then for 10+, untap and fateful showdown/gearhulk then for 10+ again, though I've done 20+ with a single showdown quite a few times. If you have fewer cards in your library then cards in hand, you'll draw the game if you kill them with a showdown.