Your search for "Card Guard SDGU-EN021" revealed the following:
Card Guard - SDGU-EN021 - Common - Unlimited from Structure Deck: Gates of the Underworld Unlimited, available at 401 Games Canada. Rarity: Common Card Text:When this card is Normal or Special Summoned, place 1 Guard Counter on it. This card...
Card Guard - SDGU-EN021 - Common - 1st Edition from Structure Deck: Gates of the Underworld 1st Edition, available at 401 Games Canada. Rarity: Common Card Text:When this card is Normal or Special Summoned, place 1 Guard Counter on it....
Number 18: Heraldry Patriarch - OP28-EN021 - Common from OTS Tournament Pack 28, available at 401 Games Canada. Rarity: Common Card Text:2 Level 4 monstersOnce per Chain, during either player's turn, if 2 or more monsters with the same name...