Cheapest priced copy (The List): $1.79 at Card Kingdom, near mint, their price list as of .
Olivia, Mobilized for War 
Legendary Creature — Vampire Knight · 3/3 · Mythic · Secret Lair Drop · #492
Flying
Whenever another creature you control enters, you may discard a card. If you do, put a +1/+1 counter on that creature, it gains haste until end of turn, and it becomes a Vampire in addition to its other types.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $1.79 to $12.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | SOI-248 | Mythic | $1.79 | — |
| Shadows over Innistrad Promos | 248s | Mythic | — | $4.49 |
| Secret Lair Drop | 492 | Mythic | $12.99 | $11.99 |
| Secret Lair Drop | 699 | Mythic | $4.49 | $2.49 |
| Shadows over Innistrad | 248 | Mythic | $1.79 | $2.99 |
3 rulings from Wizards of the Coast
- 8 April 2016If you discard a card, the creature only gains haste until end of turn, but the +1/+1 counter and Vampire subtype remain indefinitely.
- 8 April 2016If the entering creature leaves the battlefield before the triggered ability of Olivia, Mobilized for War resolves, you may still discard a card. The rest of the ability has no effect.
- 8 April 2016You decide whether to discard a card as the triggered ability of Olivia, Mobilized for War resolves. If you do, the rest of the ability’s effects happen before any player may take actions.