The Pirate one, you have to not get greedy when dropping Cookie, but you also need to be patient with Cookie--you'll need him to come out as a ridiculously overstatted minion, just don't wait too long.
Witch, I've found it to be very dependent on what spells you get. Grab a Wild Growth in your opening hand, and you're golden. (One game, I managed to get both copies in my hand, so T2 Wild Growth into T3 Wild Double Growth into an eventual GG.)
Haven't played Cat enough to evaluate.
I really really hope Witch is their way of testing out a new mechanic for an expansion (probably one coming out next year). I love mechanics that require you to puzzle-solve to use effectively, especially for Arena.