I think the legality of Psychic Pokemon directly attacking or manipulating enemies in the mental sense has been effectively banned since it's extremely broken against everything that's not Ghost or Dark. As for non-STAB users of Psychic moves they're much more limited, so I doubt the scenario you suggested can happen. The best you can do is use a Psychic blast to damage the enemy before the attack can be launched, possibly interrupting it.
This really depends on how deep the pool is, but if it's about average (one metre deep) I don't see Bulbasaur getting it off very successfully unless it's been sigged to be bigger than normal. Bulbasaur will have to move all its limbs in a bid not to sink.
I feel so embarrassed pestering you with so many ASB questions ;-; It's just that I find you an approachable and reliable source... may I ask for another opinion good sir? Sorry D: