Call for Aid is, without a doubt, the best new card in the deck
They have lots of powerful synergizing abilities, and some feature the Amass mechanic, an ability last seen in 2019's War of the Spark
It could be to pay a cost, or maybe because the effect of a spell or ability tells you to
He costs three mana (1U, 1W, 1R) and enters play as a 3/3
Getting 2/2s simply for playing Magic is a strong ability on its own, and opens up options for mana ramp, Voltron (making 1 creature super strong through powerups), Curses like Curse of Opulence for table politicking, and several other cool, unique effects that Auras can bring to the table as you build a token army
You can think about it in decks like Teysa Karlov where you sacrifice creatures but also take advantage of tokens, like with the afterlife mechanic