It wasnt because the cards were underpriced its because they were about to fall off a cliff
Fend off fiendish fungi as you crawl through the Underdark
, , Remove any number of charge counters from this artifact: It deals that much damage to any target
Try all the Evolutions and test it with all Digimons
According to ABUGames, which isnt the pricing authority on Magic but does at least have a reasonable set of listings for oversized cards, the foil oversized Gisela, Blade of Goldnight is the most valuable (around $250)
you cannot Special Summon monsters for the rest of this turn, except Fiend-Type monsters, also destroy the targeted cards, and if you do, Special Summon this card (this is a Quick Effect)