Thanks! That pesky hawk is causing a lot of problems :p I have changed the hawk so that the passive is a substantial, but hopefully non-game breaking, speed boost and then the active effect is now a powerful hawk attack. So speed boosts no longer stack. I removed Hind Legs (a speed boost powerup) from the game for now, but I think we will try to incorporate something similar to what you suggested for that card (the asymptomatic approach)!
Hopefully that's a lot of the main bugs fixed - we are focussing on bringing in more content and systems now :)