The most valuable cards from the Celebrations set typically include holographic rare cards, first edition prints, and cards featuring popular Pokemon
It has the Vedalken Orrery issue where you cross your fingers you untap with it, plus the Crucible of Worlds problem where its no longer unique
At the beginning of combat on your turn, you may have Gogo, Mysterious MimeGogo, Mysterious Mime become a copy of another creature you control until the end of the turn - but since Gogo keeps its name, you're free to copy legendary creatures too
If you do, when this creature enters, create a 1/1 token copy of it.) When this creature enters, target opponent loses 3 life unless they sacrifice a nonland permanent of their choice or discard a card
The best card is probably Termagant Swarm, once again, thanks to its value and flexibility
Kalamax, the Stormsire, featuring Brachydios from Monster Hunter 3 Generations