I've dealt with tadpoles quite a bit and here's what you should know about their impact. During combat encounters when you find tadpoles, destroying them triggers minor approval shifts from companions especially lae'zel, who gets pretty worked up about it. Whenever you reach those key moments where tadpoles are offered, rejecting them mainly affects cosmetic stuff like those black veins and eye changes you might've noticed on infected characters. The big choices that actually determine your ending happen much later around the netherbrain encounter, where timing and positioning matter way more than your earlier tadpole decisions.

The tricky part comes in act 3 with that astral-touched tadpole moment, which needs a decent wisdom check to resist but even failing here doesn't lock you out of any endings. Your final choices about controlling or destroying the netherbrain, or even triggering certain companion events still remain open regardless of how many tadpoles you've destroyed or used throughout your journey. Maybe interesting - while the emperor's dialogue shifts slightly based on your tadpole history, the core ending paths stay exactly the same