Spireside Infiltrator — ruling 1

This is a triggered ability, not an activated ability. It doesn't allow you to tap Spireside Infiltrator whenever you want; rather, you need some other way of tapping it, such as by attacking.

Spireside Infiltrator — ruling 2

For the ability to trigger, Spireside Infiltrator has to actually change from untapped to tapped. If an effect attempts to tap it, but it was already tapped at the time, this ability won't trigger.

Spireside Infiltrator : règles, fonctionnement et interactions (MTG)

Spireside Infiltrator 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

Whenever this creature becomes tapped, it deals 1 damage to each opponent.

How it works : Spireside Infiltrator

Original English text — Wizards of the Coast / Scryfall

#1September 20, 2016· Wizards of the Coast
This is a triggered ability, not an activated ability. It doesn't allow you to tap Spireside Infiltrator whenever you want; rather, you need some other way of tapping it, such as by attacking.
No other card is named in this ruling.
#2September 20, 2016· Wizards of the Coast
For the ability to trigger, Spireside Infiltrator has to actually change from untapped to tapped. If an effect attempts to tap it, but it was already tapped at the time, this ability won't trigger.
No other card is named in this ruling.