Kinscaer Sentry — ruling 1

The value of X is calculated only once, as Kinscaer Sentry's last ability resolves.

Kinscaer Sentry — ruling 2

You choose the player, planeswalker, or battle the creature you put onto the battlefield is attacking. It doesn't have to attack the same player, planeswalker, or battle as Kinscaer Sentry.

Kinscaer Sentry — ruling 3

If a card in your hand has {X} in its mana cost, X is 0 for the purpose of determining its mana value.

Kinscaer Sentry — ruling 4

Although the creatures put onto the battlefield with Kinscaer Sentry enter as attacking creatures, they were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won't trigger when the creatures enter attacking.

Kinscaer Sentry : règles, fonctionnement et interactions (MTG)

Kinscaer Sentry 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

First strike, lifelink Whenever this creature attacks, you may put a creature card with mana value X or less from your hand onto the battlefield tapped and attacking, where X is the number of attacking creatures you control.

How it works : Kinscaer Sentry

Original English text — Wizards of the Coast / Scryfall

#1November 17, 2025· Wizards of the Coast
The value of X is calculated only once, as Kinscaer Sentry's last ability resolves.
No other card is named in this ruling.
#2November 17, 2025· Wizards of the Coast
You choose the player, planeswalker, or battle the creature you put onto the battlefield is attacking. It doesn't have to attack the same player, planeswalker, or battle as Kinscaer Sentry.
No other card is named in this ruling.
#3November 17, 2025· Wizards of the Coast
If a card in your hand has in its mana cost, X is 0 for the purpose of determining its mana value.
No other card is named in this ruling.
#4November 17, 2025· Wizards of the Coast
Although the creatures put onto the battlefield with Kinscaer Sentry enter as attacking creatures, they were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won't trigger when the creatures enter attacking.
No other card is named in this ruling.