It's wise not to disturb an artist at work.

Reclusive Artificer

Haste (This creature can attack and {T} as soon as it comes under your control.)
When this creature enters, you may have it deal damage to target creature equal to the number of artifacts you control.

The List

Duel Decks: Elves vs. Inventors

Haste
When Reclusive Artificer enters the battlefield, you may have it deal damage to target creature equal to the number of artifacts you control.

Magic Origins

Haste (This creature can attack and {T} as soon as it comes under your control.)
When Reclusive Artificer enters the battlefield, you may have it deal damage to target creature equal to the number of artifacts you control.

Count the number of artifacts you control as Reclusive Artificer’s triggered ability resolves to determine how much damage it deals.

If you are the only player who controls a creature when Reclusive Artificer’s second ability triggers, you must choose one of those creatures as the target, although you can choose to not deal it damage.