Historical Rules · 5 February 2021
Rule 702.37a
Official source text from the 5 February 2021 Rules release
Amplify is a static ability. “Amplify N” means “As this object enters the battlefield, reveal any number of cards from your hand that share a creature type with it. This permanent enters the battlefield with N +1/+1 counters on it for each card revealed this way. You can’t reveal this card or any other cards that are entering the battlefield at the same time as this card.”