Cheapest priced copy (Commander Legends: Battle for Baldur's Gate): $9.99 at Card Kingdom, near mint, their price list as of .
Aboleth Spawn 
Creature — Fish Horror · 2/3 · Rare · Commander Legends: Battle for Baldur's Gate · #612
Flash
Ward {2}
Probing Telepathy — Whenever a creature entering under an opponent's control causes a triggered ability of that creature to trigger, you may copy that ability. You may choose new targets for the copy.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $9.99 to $10.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends: Battle for Baldur's Gate | 612 | Rare | $10.99 | — |
| Commander Legends: Battle for Baldur's Gate | 662 | Rare | $9.99 | — |
| The List | CLB-662 | Rare | — | — |
6 rulings from Wizards of the Coast
- 10 June 2022Aboleth Spawn's ability cares only about triggered abilities of the creature that's entering, not abilities of other permanents that trigger when that creature enters the battlefield.
- 10 June 2022Triggered abilities use the words "when," "whenever," or "at." They're often written as "[Trigger condition],[effect]."
- 10 June 2022If the ability is modal (that is, it has a bulleted list of choices), the copy will have the same mode(s). You can't choose new ones.
- 10 June 2022Effects that modify how a creature enters the battlefield are not triggered abilities and are not affected by Aboleth Spawn's ability. These include (but aren't limited to) entering the battlefield as a copy of another permanent, entering the battlefield with counters, and entering the battlefield tapped.
- 10 June 2022Aboleth Spawn's ability will always go on the stack on top of the entering creature's triggered ability that caused it to trigger. The copy it creates will be created on the stack on top of the entering creature's triggered ability and the copy will resolve before that ability.
- 10 June 2022The copy will have the same targets as the ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).