Cheapest priced copy (Tarkir: Dragonstorm): $0.49 at Card Kingdom, near mint, their price list as of .
Mardu Siegebreaker 
Creature — Human Warrior · 4/4 · Rare · Tarkir: Dragonstorm · #206
Deathtouch, haste
When this creature enters, exile up to one other target creature you control until this creature leaves the battlefield.
Whenever this creature attacks, for each opponent, create a tapped token that's a copy of the exiled card attacking that opponent. At the beginning of your next end step, sacrifice those tokens.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
4 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Tarkir: Dragonstorm Promos | 206p | Rare | $0.59 | $0.99 |
| Tarkir: Dragonstorm Promos | 206s | Rare | — | $1.99Out of stock |
| Tarkir: Dragonstorm | 206 | Rare | $0.49 | $1.49 |
| Tarkir: Dragonstorm | 364 | Rare | $1.29 | $2.49 |
7 rulings from Wizards of the Coast
- 4 April 2025Any “enters” abilities of the copied card will trigger when the tokens enter. Any “as this creature enters” or “this creature enters with” abilities of the copied card will also work.
- 4 April 2025If a token is exiled with Mardu Siegebreaker’s third ability, it will cease to exist and won’t return to the battlefield. Mardu Siegebreaker’s last ability won’t create copies of that token.
- 4 April 2025Auras attached to the exiled creature will be put into their owners’ graveyards. Any Equipment will become unattached and remain on the battlefield. Any counters on the exiled creature will cease to exist. When the card returns to the battlefield, it will be a new object with no connection to the card that was exiled.
- 4 April 2025If the exiled card isn’t a creature card, the token copies will still be created and they’ll still enter tapped. They just won’t be attacking.
- 4 April 2025Although the tokens enter attacking, they were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won’t trigger when those tokens enter attacking.
- 4 April 2025If Mardu Siegebreaker leaves the battlefield before its “enters” ability resolves, the target creature won’t be exiled.
- 4 April 2025The token copies what’s printed on the exiled card and nothing else. It doesn’t copy any effects that changed its characteristics before it was exiled.