Theres also a limit noted saying a player could only buy it three times

View as Gallery View as List C Common C Common C Common C Common C Common C Common C Common C Common UR Ultra Rare UR Ultra Rare SR Super Rare SR Super Rare SR Super Rare C Common C Common C Common C Common C Common C Common C Common SR Super Rare C Common C Common SR Super Rare SE Secret Rare C Common SE Secret Rare STAR Starlight Rare SR Super Rare UR Ultra Rare C Common C Common SE Secret Rare C Common C Common UR Ultra Rare SR Super Rare SE Secret Rare STAR Starlight Rare SE Secret Rare C Common C Common SR Super Rare UR Ultra Rare UR Ultra Rare UR Ultra Rare SR Super Rare UR Ultra Rare STAR Starlight Rare SE Secret Rare C Common C Common UR Ultra Rare SR Super Rare C Common C Common C Common SR Super Rare SR Super Rare STAR Starlight Rare SR Super Rare SR Super Rare C Common C Common C Common SE Secret Rare C Common C Common UR Ultra Rare SR Super Rare UR Ultra Rare SR Super Rare C Common C Common C Common UR Ultra Rare C Common C Common SR Super Rare C Common SR Super Rare SR Super Rare SE Secret Rare SE Secret Rare C Common SR Super Rare SR Super Rare C Common C Common C Common C Common SE Secret Rare SR Super Rare UR Ultra Rare C Common SR Super Rare C Common C Common C Common SR Super Rare SR Super Rare SR Super Rare UR Ultra Rare C Common STAR Starlight Rare Piwraithe the Ghost Pirate X WATER Level 4 [ AquaEffect ] ATK 1500 DEF 500 If a face-up WATER monster(s) you control, except "Piwraithe the Ghost Pirate", is destroyed by battle or card effect, while this card is in your GY: You can Special Summon this card (but banish it when it leaves the field), and if you do, it gains 100 ATK for each WATER monster in your GY, until the end of the next turn

Lower Text - Promo Info BOOSTER VS ROYAL KNIGHT [BT-13] CLOSECLOSE BT13-093 U Digimon Lv.4 Omekamon Color White Form Champion Attribute Data Type Puppet/X Antibody DP 4000 Cost 4 Digivolve Cost 1 - Digivolve Cost 2 - Upper Text [On Play] Draw 1 (Draw 1 card from your deck.) [On Deletion] Place 1 Digimon card with the [Royal Knight] trait from your hand as the bottom digivolution card of one of your [King Drasil_7D6] in the breeding area
This allows you to sacrifice it, do damage, and revive it infinitely
A lot of these combos, as far as function goes, already existed