In Modern, its a great way to get your mill-friendly creatures stronger
These combos work best in a deck that's aiming to pay a bunch of life, like K'rrik, Son of Yawgmoth
Strengths and Weaknesses Strong Versus
Whats great about it is that it doesnt just let you play cards for free from among those you exile with its first ability, but it also serves as a payoff as every time you cast a spell you dont own, you get a 3/3 demon token as a souvenir
Anyway, Arcane Proxy is a worse Snapcaster Mage, mainly since the lack of flash and the on cast trigger eliminating the option to blink it overtakes the ability to play the targeted spell for free
We ended up making an enchantment that enters and gives you two 2/2 black Zombie creature tokens and then lets you spend mana to turn dead creature cards from any graveyard into Zombies