To beat Tread Lightly: Your character becomes fatter when landing, so constantly hold the up button, and you'll be less likely to trigger nearby buttons.
It's just a matter of clearing out the extras for most bosses and then taking the bosses out one on one, standing just above or below them. For the end boss, stand way away, lure the zombies to you, then dash over and plow the boss into the ground. For the zamboni, serpentine in wide up and down streaks.