Cheapest priced copy (Ikoria: Lair of Behemoths): $0.49 at Card Kingdom, near mint, their price list as of .
Slitherwisp 
Creature — Elemental Nightmare · 3/2 · Rare · Ikoria: Lair of Behemoths · #208
Flash
Whenever you cast another spell that has flash, you draw a card and each opponent loses 1 life.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ikoria: Lair of Behemoths | 208 | Rare | $0.49 | $0.79 |
| Ikoria: Lair of Behemoths | 345 | Rare | $1.99 | $1.49 |
| Ikoria: Lair of Behemoths Promos | 208p | Rare | $0.59 | $2.99 |
| Ikoria: Lair of Behemoths Promos | 208s | Rare | — | $0.69 |
4 rulings from Wizards of the Coast
- 17 April 2020If an effect allows you to cast a spell “as though” it has flash, Slitherwisp’s last ability won’t trigger.
- 17 April 2020In a Two-Headed Giant game, Slitherwisp’s last ability causes the opposing team to lose 2 life and you to draw one card.
- 17 April 2020An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
- 17 April 2020Players can cast spells and activate abilities after the triggered ability resolves but before the spell that caused it to trigger does.