Technically I love both Koma's, which includes the newer Koma, World-Eater, but I think it's widely accepted that the Cosmos Serpent is the better of the two legendary serpents
The CCC Grading advantage 14 TCGs We master many TCG : Pokmon , Yu-Gi-Oh , Magic: The Gathering (MTG), Dragon Ball Super , Vanguard Cardfight, Force of Will , Flesh and Blood , Harry Potter TCG, One Piece Card Game, Dragon Ball Carddass, DB Heroes, Disney Lorcana, Naruto Kayou, Metazoo
The cost is very clear: putting two rares in for one means that you double your money on "true bulk" while your trading partner gets to swap two useless cards for one that they want
Crash the Ramparts: Limited battle trick
Other Pokmon cards that players should pick up for cheap can be Salazle GX, Latios EX, and even Gumshoos GX