This is an interesting restriction that makes this card feel very well-balanced
A handful make use of half mana, and the sets typically feature uncommon creature types like clams, donkeys, or beebles
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
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
Wayfarer's Bauble is a bit better than Prismatic Lens as a mana artifact