You blink any number of non-lands you control, not just creatures, so Ichor Wellspring in artifacts, Mulldrifter in creatures, or Flight of Fancy in enchantments will all work
The enemy-color legendary creatures from Invent Superiority and Entropic Uprising give us four different partner configurations that are also Four-Color Not Black
That said, the planeswalkers given the critter treatment are certainly more interesting than the non-species swapped cards, so that might help keep the price propped up
Reprints of Vial Smasher the Fierce and Witchs Clinic were welcome, too
We have Bleachbone Verge, Riverpyre Verge, Sunbillow Verge, Wastewood Verge, and Willowrush Verge, and they're all preselling for $7-$8
So, at the beginning of your upkeep, you reveal the top card of your deck, and if it matches a Creature type you have in play, you get to cast it for free