Any player may activate this ability
However, the fact that you can use the creature you created to trigger the haunt ability again makes it worth destroying two problematic creatures, as the 1/1 is likely more prone to dying
The experience counter goes on you, the player, not on Aang
Another Mega Evolution set, another Mega Hyper Rare
Even if you wanted to play a standard game with this, the only fun part is mixing 3 differnet decks of your choice together, but the unfun part is the lack of good cards to pull you into the game
The key thing to build around is the other than your hand line, so cards with foretell (Behold the Multiverse, Delayed Blast Fireball) and flashback (Think Twice, Galvanic Iteration) are excellent