Cheapest priced copy (Ravnica: Clue Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Kraul Harpooner 
Creature — Insect Warrior · 3/2 · Uncommon · Ravnica: Clue Edition · #167
Reach
Undergrowth — When this creature enters, choose up to one target creature you don't control with flying. This creature gets +X/+0 until end of turn, where X is the number of creature cards in your graveyard, then you may have this creature fight that creature.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.35 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ravnica: Clue Edition | 167 | Uncommon | $0.35 | — |
| Guilds of Ravnica | 136 | Uncommon | $0.35 | $2.49 |
| Jumpstart 2022 | 683 | Uncommon | $0.35 | — |
| The List | GRN-136 | Uncommon | $0.35 | — |
6 rulings from Wizards of the Coast
- 5 October 2018Creature cards with other types, such as artifact creature cards, count for undergrowth abilities.
- 5 October 2018Because tokens aren't cards, they never count for undergrowth abilities.
- 5 October 2018If you don't choose a target creature, Kraul Harpooner simply gets +X/+0 until end of turn.
- 5 October 2018If you choose a target and the target creature is an illegal target when Kraul Harpooner's ability tries to resolve, the ability doesn't resolve and Kraul Harpooner doesn't get +X/+0. If the target creature is legal but Kraul Harpooner is no longer on the battlefield, the target creature won't deal or be dealt damage.
- 5 October 2018The value of X is determined only as the undergrowth ability resolves. If the number of creature cards in your graveyard changes later in the turn, Kraul Harpooner is unaffected.
- 5 October 2018You choose the target of the triggered ability (or that it has no target) as it goes on the stack, but you choose whether the creatures fight as that ability resolves.