Then put all cards exiled this way that weren't cast on the bottom of your library in a random order." A spell's mana value is determined only by its mana cost
(Also shuffle this card.) If Bloomvine Regent enters at the same time as one or more other Dragons you control, its triggered ability will trigger for each of those Dragons, including itself
Caldera Hellion If youre playing blink with access to red, Caldera Hellion can be sooooo obnoxious
Its a great partner with pair, with Yannik as the support piece and Nikara as the payoff
Olivia, Opulent Outlaw is the closest the color combination really has to offer at time of writing, and even that is going to be more about outlaws and Treasures, only using +1/+1 counters as a reward to help finish things off
Note that Wizards has made an official statement that non-factory cut cards meet the "genuine and published by Wizards of the Coast" criterion, so their legality will just depend on whether they meet the other criteria in the opinion of the head judge