Damn, if I only knew this earlier I couldve saved so much money on my collection
Officially, it's not legal in Eternal MTG formats - namely Legacy, Vintage, Pauper, and Commander
This probably wouldnt matter to most, but it certainly matters to a collector trying to collect a complete set of all 350/350 cards from 8th Edition, for example
It being a transformed creature already prevented an infinite combo with Restoration Angel, but the mana requirement does slow Reflection of Kiki-Jiki down a lot
The first two lines of text here have been done before, with cards like Realmwalker, Vivien, Monsters Advocate, and Vizier of the Menagerie
If an activated ability of a card in exile with a brain counter on it references the card it's printed on by name, treat Rex's version of that ability as though it referenced Rex, Cyber-Hound instead