If you can manage it, the card then transforms into World Champion, Celestial Weapon, a powerful equipment
This means it can activate as many times as you want once you have your combo assembled
Triskaidekaphile is probably worth a slot since putting lands into your hand at instant speed could creep you up to thirteen cards and the win condition, and other than that, the card draw ability and no maximum hand size are going to be useful
After the sticker is put on, any new effects that change the creature's base power and toughness will apply as normal, and when those effects expire, the creature will revert to the base power and toughness set by the sticker
The strategy is simple: Cast big dragons, and get Atarka on the board to give them double strike
This will be absolutely amazing in Lizard decks, but the +1/+1 ability is relevant for any deck that can get creatures in for combat damage