mtg card font At the beginning of each players draw step Font of Return

If you flip a second Illuna, you can add it to hand and then mutate it onto the first one for a double trigger (and no legend rule!) Its harder to see exactly what to do with Vadrok, Apex of Thunder , since one of the best spells in Jeskai to recast Deafening Clarion will also kill Vadrok unless you mutate it under something with better stats

However, there are caveats

The reason its above the others on the list is that its part of an obnoxious combo with Kiki-Jiki, Mirror Breaker

Other options may not exactly combo with themselves, but the other combo pieces needed are so generic that it might as well be a 1-card combo

Even within the Champions block, that's awfully narrow, and in Magic as a whole, it is hopelessly irrelevant