yugioh duel academy decks Trading Card Game Speed GX Duel Box Set [8 Complete Decks] : Toys & Games Skill Cards may only be used in Speed Duel. Duel Academy (card) | Yu-Gi-Oh!

As proxy cards are made from actual cheaper bulk common Magic the Gathering cards, they will still have the same back as the normal cards

Most spells with this mechanic have bolster 1, but the counter goes up to bolster 5 in the case of Steppe Mastodon

Comicbook.com

During your opponent's Main Phase (Quick Effect): You can detach 2 materials from this card (or just 1 material if all this card's materials are Xyz Monsters), then target 1 Attack Position monster your opponent controls or 1 monster in their GY

See the full breakdown per format in the Legality section above.

With striking artwork and notable cachet due to being a chase card from the set upon its release, its no surprise to see this Angel worth over $5 on the secondary market