i don't run the in browser version so i don't really know

I think you experienced a glitch where the two ducks (athletic and strength) get stuck together in some of the adult trainings

I can't decide on what are the best strategy's to do jumping 2

the only ones I've seen that seem to be impossible are sandbox 0 sandbox 2 and the sky levels though I haven't tried to much of the sky levels

jumping and spamming crouch let's you move

I tried it and the tutorial at least is possible