Cheapest priced copy (Foundations Commander): $1.29 at Card Kingdom, near mint, their price list as of .
Leyline Tyrant 
Creature — Dragon · 4/4 · Mythic · Tarkir: Dragonstorm Commander · #221
Flying
You don't lose unspent red mana as steps and phases end.
When this creature dies, you may pay any amount of {R}. When you do, it deals that much damage to any target.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $1.29 to $7.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Foundations Commander | 162 | Mythic | $1.29 | — |
| Zendikar Rising Promos | 147p | Mythic | $3.49 | $6.99 |
| Zendikar Rising Promos | 147s | Mythic | — | $7.99 |
| Tarkir: Dragonstorm Commander | 221 | Mythic | $2.49 | — |
| Zendikar Rising | 147 | Mythic | $2.79 | $3.99 |
| Zendikar Rising | 348 | Mythic | $6.49 | $4.99 |
4 rulings from Wizards of the Coast
- 25 September 2020Once Leyline Tyrant leaves the battlefield, you have until the end of the current step or phase to spend your unspent red mana before it is lost as normal. There is no penalty associated with this other than the loss of the mana.
- 25 September 2020If a red mana you add has certain restrictions or riders associated with it (for example, if it was produced by Base Camp), they'll apply to that mana no matter when you spend it.
- 25 September 2020You can keep unspent red mana indefinitely while Leyline Tyrant is on the battlefield. That means if you add a red mana during one step or phase, you can spend it during a later step or phase, or even a later turn. Other types of mana will continue to be lost as normal as each step and phase ends.
- 25 September 2020Leyline Tyrant's last ability goes on the stack without a target. While that ability is resolving, you may pay any amount of red mana, including from the unspent mana you have. If you do, a second ability triggers and you pick one target to be dealt that much damage. This is different from abilities that say "If you do . . ." in that players may cast spells and activate abilities after mana is paid but before the damage is dealt.