Cheapest priced copy (Dominaria United Commander): $8.49 at Card Kingdom, near mint, their price list as of .
Sivitri, Dragon Master 
Legendary Planeswalker — Sivitri · Mythic · Dominaria United Commander · #43
+1: Until your next turn, creatures can't attack you or planeswalkers you control unless their controller pays 2 life for each of those creatures.
−3: Search your library for a Dragon card, reveal it, put it into your hand, then shuffle.
−7: Destroy all non-Dragon creatures.
Sivitri, Dragon Master can be your commander.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $8.49 to $9.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria United Commander | 43 | Mythic | $8.49 | $9.99 |
| Dominaria United Commander | 65 | Mythic | — | — |
2 rulings from Wizards of the Coast
- 9 September 2022A player who controls a creature that “attacks if able” can decline to pay additional costs to have that creature attack. If they do and there’s no other player or planeswalker to attack, that creature simply doesn’t attack.
- 9 September 2022In a Two-Headed Giant game, creatures can attack your teammate and planeswalkers your teammate controls without requiring a life payment.