Cheapest priced copy (Shadows over Innistrad Promos): $0.49 at Card Kingdom, foil, near mint, their price list as of .
Elusive Tormentor // Insidious Mist 
Creature — Vampire Wizard // Creature — Elemental · 4/4 · Rare · Shadows over Innistrad · #108
{1}, Discard a card: Transform this creature.
Hexproof, indestructible
This creature can't block and can't be blocked.
Whenever this creature attacks and isn't blocked, you may pay {2}{B}. If you do, transform it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 to $0.59 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Shadows over Innistrad Promos | 108 | Rare | — | $0.49 |
| Shadows over Innistrad Promos | 108s | Rare | — | $0.59 |
| Shadows over Innistrad | 108 | Rare | $0.49 | $0.49 |
3 rulings from Wizards of the Coast
- 8 April 2016You can activate Elusive Tormentor's ability multiple times to discard multiple cards. Only the first instance of the ability to resolve will cause it to transform.
- 8 April 2016Once blockers have been chosen, transforming Elusive Tormentor into Insidious Mist won't cause it to become unblocked.
- 8 April 2016You can, all within one turn, attack with Elusive Tormentor, transform it into Insidious Mist before blockers are chosen, transform it back as its triggered ability resolves, and have it deal 4 combat damage.