Lenora, mostly because I just didn't have any fast Fighting types at that point in the game to dispatch that Watchog before it used Retaliate. Elesa was a pain in the neck, too, but I wouldn't say that she was hard to beat, though...
I'd want to be a Swampert, mostly because I think that it'd be interesting to be able to just dive and chill in the water without fear of drowning, but accessibility to land would also be nice. Plus, Swampert is solid and strong, which is nothing to really complain about. Plus, Swampert's my...
My personal favorites atm are Krookodile and Snivy. I just really like the personalities of the two. Although, when it comes to memorability, Oshawott definitely takes the cake.
No, I haven't heard of that entity. That sounds pretty unique.
I like many Poison types for their looks, but their stats, not so much. But, few Poisons actually have decent type coverage, but often don't have the stats to back it up (Arbok). In my opinion, Poison types usually get the shaft...