If you're unsure if any of your cards are of value, you can use this nifty tool at CardMavin to check
For instance, when the new Simba card boosts, the player reveals the top card of the deck
Unlike the Scarlet & Violet Megas, which give a whopping three prize cards when knocked out, the XY Megas only gave up two prize cards
Try to collect them all and discover the different cards available in the expansions
Cast Mana Geyser, and while its on the stack, cast Reiterate with buyback to copy Mana Geyser
Ashcoat of the Shadow Swarm is probably the only real competition Karumonix has, and it might be better depending on your particular rat build