The other card, Mishra, Claimed by Gix doesn't do much in a dragon tribal deck, but it IS just four mana, and it works off attacking creatures, fitting into a low curve deck if you really want the meld
Promise offers more bodies per mana and bodies per card than any other low cost token producer
Youre playing with strange cards and unpredictability to keep your opponents off-kilter until you find a way to squeeze out an utterly nonsensical win or go out with a bang
They must sacrifice something, even if all they have is a three-cost planeswalker
I dont like giving opponents the choice on a card because they will always choose the best option for them, rather than the best option for you
That's nice and all, but its really the mana cost that makes Sigarda's Aid a powerhouse in multiple formats