Scoria Wurm - Not that exciting, but its a cheap threat that you could hopefully keep alive longer with Krark's Thumb Mirror March - This can get out of hand really quickly, and there's basically no downside to losing flips Yusri, Fortune's Flame - Designed to be a commander, but it's a solid card to include in the 99 as well Goblin Traprunner - Tons of easy flips with no downsides Squee's Revenge - Can be a huge card draw Planar Chaos - This one can be a bit annoying and might only be good if you also have Krark's Thumb, but it lets you play more controlling Krark, the Thumbless - Similar to Planar Chaos, use at your own risk Frenetic Efreet and Frenetic Sliver - A single card that lets you flip as many coins as you want (you can activate the ability as many times as you want before you let any of the activations resolve, and then even if he dies you still flip all the coins) Puppet's Verdict - A sweeper that let's you control what to kill if you can manipulate the flip As for other cards that I think could fit the strategy of the deck, I would focus on ways to multiply your other effects (extra upkeep steps, copying your permanents, doubling your abilities, etc)

Issue is, all of these printings were US-only, with even the European release of Dawn of Destiny replacing Ra with a different promo card, Mesmeric Control
Tropical Rainforest Jaguar Lair doesnt really work as youll probably be removing damaged characters
Finished up the XY gold border secret rares
The recent promo Nissa, Resurgent Animist, for example, is sold out at Hareruya for $210 at the time of writing