Your search for "Crystron Sulfefnir RATE-EN021" revealed the following:
Crystron Sulfefnir - RATE-EN021 - Super Rare - 1st Edition from Raging Tempest 1st Edition, available at 401 Games Canada. Rarity: Super Rare Card Text:If this card is in your hand or Graveyard: You can discard 1 "Crystron" card, except...
Crystron Sulfefnir - OP27-EN016 - Common - Unlimited from OTS Tournament Pack 27, available at 401 Games Canada. Rarity: Common Card Text:If this card is in your hand or GY: You can discard 1 "Crystron" card, except "Crystron Sulfefnir"; Special...
Crystron Sulfefnir - RATE-EN021 - Super Rare - Unlimited from Raging Tempest Unlimited, available at 401 Games Canada. Rarity: Super Rare Card Text:If this card is in your hand or Graveyard: You can discard 1 "Crystron" card, except "Crystron Sulfefnir";...