The side deck was primarily built for Gouki and the mirror match, as evidenced by the inclusion of PSY-Framegear Gammas, Mind Controls and Super Polymerization
These cards start off as item Pokemon fusion cards that have all the aspects of an item card before you place them down, but they are treated as a Pokemon once you Bench them
But at a glance (right now), it doesn't seem to be as impactful as some other Room cards we've seen
Being able to pull out from the opponent's Graveyard offers Zombie World synergy, but to rein in potential combos and keep them temporarily vulnerable, they come back with 0 DEF in Defense Position, and there's a once-per-turn-per-copy clause to prevent Box from indefinitely reviving itself
You can hold a maximum of 2 booster packs, so open them right away to make room for the next one
Plus it ramps you into more Thallids when the time finally comes