Cheapest priced copy (Aetherdrift): $0.49 at Card Kingdom, near mint, their price list as of .
Momentum Breaker 
Enchantment · Uncommon · Aetherdrift · #97
Start your engines! (If you have no speed, it starts at 1. It increases once on each of your turns when an opponent loses life. Max speed is 4.)
When this enchantment enters, each opponent sacrifices a creature or Vehicle of their choice. Each opponent who can't discards a card.
{2}, Sacrifice this enchantment: You gain life equal to your speed.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
1 printing · $0.49 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Aetherdrift | 97 | Uncommon | $0.49 | $0.99 |
6 rulings from Wizards of the Coast
- 7 February 2025Each player tracks their speed (or lack thereof) separately. Increasing your speed has no effect on whether another player has speed.
- 7 February 2025“Max speed — [ability]” means “As long as you have max speed, this object has [ability].” If the granted ability functions in a zone other than the battlefield, the max speed ability does too.
- 7 February 2025Your speed doesn’t change until a spell or ability says so, such as the inherent triggered ability that cares about opponents losing life during your turn. Notably, losing control of permanents with start your engines! doesn’t affect your speed.
- 7 February 2025A player “has max speed” if their speed is 4.
- 7 February 2025If an effect needs to know what a player’s speed is and that player doesn’t have a speed, their speed is considered 0.
- 7 February 2025Start your engines! isn’t a triggered ability. Increasing your speed to 1 is something that happens as a state-based action as soon as you control a permanent with the ability. Notably, this includes gaining control of a permanent with the ability that another player controls.