The Xenoskin zipfolios outdo other folders for one simple reason: they zip shut
Not only can you do that, but you can devolve it with Devolution Spray (DRX 113/124), and then evolve it again immediately with the stadium, and you can scoop it up with Super Scoop Up (FFI 100/111) and then evolve it again immediately with the stadium
More recent releases with unique cards or exciting alternate art are typically much more valuable than others
I just finished all of the challenges and wish there were more
Most Commander decks have enough targeted removal to destroy your creature once or twice, but locking the Greaves on it basically ensures theyll have to two-for-one you (perhaps Shattering the Greaves then destroying your creature) or board wipe
Baby Pokemon like Mantyke also appear, which fit the mini-expansions theme, even though this Pokemon was introduced in later games than Pokemon Gold and Silver