Rule 811.1.d.5

If a hidden spell or a play effect of a hidden permanent causes you to play a unit, you must choose to play that unit at that battlefield.

Rulings that cite this rule

• If I play a card I hid, and that cardʼs effects include playing additional units (for example, tokens), can I play them anywhere?
• When you play a card from hidden, it gains several additional restrictions. The rules were somewhat unclear on this.

Official Core Rules