Cheapest priced copy (Commander Legends: Battle for Baldur's Gate): $0.49 at Card Kingdom, near mint, their price list as of .
Mardu Strike Leader 
Creature — Human Warrior · 3/2 · Rare · Fate Reforged · #75
Whenever this creature attacks, create a 2/1 black Warrior creature token.
Dash {3}{B} (You may cast this spell for its dash cost. If you do, it gains haste, and it's returned from the battlefield to its owner's hand at the beginning of the next end step.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends: Battle for Baldur's Gate | 761 | Rare | $0.49 | — |
| Fate Reforged | 75 | Rare | $0.49 | $0.79 |
| Fate Reforged Promos | 75s | Rare | — | $0.69 |
4 rulings from Wizards of the Coast
- 24 November 2014You don't have to attack with the creature with dash unless another ability says you do.
- 24 November 2014If you choose to pay the dash cost rather than the mana cost, you're still casting the spell. It goes on the stack and can be responded to and countered. You can cast a creature spell for its dash cost only when you otherwise could cast that creature spell. Most of the time, this means during your main phase when the stack is empty.
- 24 November 2014If a creature enters the battlefield as a copy of or becomes a copy of a creature whose dash cost was paid, the copy won't have haste and won't be returned to its owner's hand.
- 24 November 2014If you pay the dash cost to cast a creature spell, that card will be returned to its owner's hand only if it's still on the battlefield when its triggered ability resolves. If it dies or goes to another zone before then, it will stay where it is.