Throatseeker — ruling 1

Throatseeker’s effect applies only after blockers have been declared. Before then, attacking creatures are neither blocked nor unblocked.

Throatseeker — ruling 2

If an unblocked attacking Ninja you control leaves combat (most likely because the combat phase has ended), it no longer has lifelink.

Throatseeker : règles, fonctionnement et interactions (MTG)

Throatseeker 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

Unblocked attacking Ninjas you control have lifelink.

How it works : Throatseeker

Original English text — Wizards of the Coast / Scryfall

#1June 14, 2019· Wizards of the Coast
Throatseeker’s effect applies only after blockers have been declared. Before then, attacking creatures are neither blocked nor unblocked.
No other card is named in this ruling.
#2June 14, 2019· Wizards of the Coast
If an unblocked attacking Ninja you control leaves combat (most likely because the combat phase has ended), it no longer has lifelink.
No other card is named in this ruling.