This power is redundant in 1v1, but in a multiplayer format, it offers a player a way to bypass the usual rules and sweep a win, forcing an interesting dynamic where other players need to protect Shinryus target
Basically, any pack which contains booster packs and a few specific Pokmon cards, such as Premium Collections featuring specific characters, are intended for use either by collectors or players who just need to bolster, or improve, the selection of cards they have available to customise their deck with
The deck focuses on enchanting your opponents with a ton of different curses, each of which have strong abilities such as draining life, card draw, removal, nerfing their creatures, direct damage, copying their spells, creating creature tokens, etc
This is very blatantly illegal, so theres a lot of opaqueness around the sellers since they constantly need to make new listings as old ones are shut down