Sparktongue Dragon — ruling 1

You don't choose a target for Sparktongue Dragon's last ability at the time it triggers. Rather, a second "reflexive" ability triggers when you pay {2}{R} this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.

Sparktongue Dragon : règles, fonctionnement et interactions (MTG)

Sparktongue Dragon is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flying When this creature enters, you may pay . When you do, it deals 3 damage to any target.

How it works : Sparktongue Dragon

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2020· Wizards of the Coast
You don't choose a target for Sparktongue Dragon's last ability at the time it triggers. Rather, a second "reflexive" ability triggers when you pay this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.
No other card is named in this ruling.