Cheapest priced copy (The Lost Caverns of Ixalan): $0.49 at Card Kingdom, near mint, their price list as of .
Stalactite Stalker 
Creature — Goblin Rogue · 1/1 · Rare · The Lost Caverns of Ixalan · #122
Menace
At the beginning of your end step, if you descended this turn, put a +1/+1 counter on this creature. (You descended if a permanent card was put into your graveyard from anywhere.)
{2}{B}, Sacrifice this creature: Target creature gets -X/-X until end of turn, where X is this creature's power.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
4 printings · $0.49 to $1.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Lost Caverns of Ixalan | 122 | Rare | $0.49 | $0.79 |
| The Lost Caverns of Ixalan | 370 | Rare | $0.49 | $0.79 |
| The Lost Caverns of Ixalan Promos | 122p | Rare | $0.49 | $0.79 |
| The Lost Caverns of Ixalan Promos | 122s | Rare | — | $1.79 |
8 rulings from Wizards of the Coast
- 10 November 2023Stalactites are the ones that hang from the ceilings of caves. You might be thinking of stalagmites.
- 10 November 2023In either case, it doesn't matter if those cards are still in that player's graveyard.
- 10 November 2023Abilities that begin with "At the beginning of your end step, if you descended this turn" will trigger only once during your end step, no matter how many times you descended this turn. However, if you haven't descended this turn as your end step begins, the ability won't trigger at all. It's not possible to put a permanent card into your graveyard during the end step in time to have the ability trigger.
- 10 November 2023Use Stalactite Stalker's power as it last existed on the battlefield to determine the value of X.
- 10 November 2023Some cards refer to the number of times a player descended this turn. Those cards care about the number of permanent cards put into that player's graveyard from anywhere this turn.
- 10 November 2023Multiple cards have abilities that begin with "At the beginning of your end step, if you descended this turn." These cards don't need to have been under your control at the time you descended. For example, if a permanent card is put into your graveyard during your first main phase and you cast Stalactite Stalker your second main phase, its ability will trigger at the beginning of your end step.
- 10 November 2023A permanent card is an artifact, battle, creature, enchantment, land, or planeswalker card. Tokens are not cards, and while tokens are put into the graveyard before ceasing to exist, that action doesn't count as a player having descended.
- 10 November 2023Some cards refer to a player who has "descended this turn." This means that a permanent card has been put into that player's graveyard from anywhere this turn.