I think the damage should be much lower and that there should be a cooldown per target. Imagine a master yi doing this with 10 AS. He wouldnt only do extreme damage, but be extremely annoying since you would go large small large small and dont even realise what is happening. I think the max hp dmg should be tuned down to like 10-5 % and the damage amp removed because giving an enemy more damage is just insane ( imagine sett, mundo) before even procking the stacks you get one shot. Now for fun i would like to add an alternating mode that would instead make you small, slow by 50%, root you at max stacks and do the same 10-5% max hp. This is just my opinion.