Whenever a creature you control with a +1/+1 counter on it attacks, double the number of +1/+1 counters on it
The only other Magic cards that tranform multiple permanents are Tovolar, Dire Overlord, which is restricted to human werewolves, and Glissa, Sunslayer and The Argent Etchings, which are restricted to Incubator tokens
Specifically, two other versions of Niv-Mizzet
If the player is facing off against someone who doesn't use many items or actions, this card can also simply be inked so that others may be used instead, and therefore, is a good defensive card to have in the deck
Its Swords to Plowshares on a stick, which means flicker decks can have a field day controlling the board with Displacer Kitten, Thassa, Deep-Dwelling, and anything else that lets them flicker it
It also helps that Celebi ex is a Basic Pokemon and Aerodactyl only requires the fairly common Amber Fossil to see play