If Pyke Returned is played hidden on Rockfall Path, does he go to base?

No, your Pyke, Returned does not go to your base. If you attempt to play a hidden unit (including Pyke, Returned) at a battlefield like Rockfall Path that prohibits playing units, the attempt is an illegal activation.

Here is the breakdown of why this occurs:

1. The Rule Interaction

• Hidden Placement: According to Rule 811.1.b and Rule 811.1.d.1, a card hidden via the Hidden keyword must be played to the specific battlefield where it is hidden.
• Battlefield Restrictions ("Can't beats Can"): While the Hidden keyword gives you permission to play the card, battlefield restrictions (such as those on Rockfall Path) act as a prohibition. Per RiftJudge FAQ #68, the "can't" restriction of the battlefield overrides the "can" permission of playing a card from Hidden.
• No Override for Units: While Rule 811.1.d.1.a provides a specific override for hidden gear to be played to a battlefield (instead of the base), there is no such override for units. Units must respect the playing restrictions of the location they are at.

2. The Consequence of Illegal Activation

According to RiftJudge FAQs #6500, #9325, and #10492:

1. Illegal Attempt: Because Rockfall Path prevents playing units, attempting to reveal and play Pyke, Returned from there is an illegal activation.
2. Rewind: The game state is immediately rewound to the moment before you attempted to play the unit.
3. Result: The card remains hidden and facedown at the battlefield. It is not moved to your base, and the action to play it fails.
4. Consequence: Because you cannot play it, the card remains stuck there. If you later lose control of that battlefield (e.g., if your other units there leave and you lose the battlefield), the hidden Pyke, Returned will be sent to the trash during the next cleanup (Rule 107.3.d).

Summary: You cannot play the unit to the battlefield, and it does not move to your base. The attempt simply results in an illegal activation, leaving the card hidden at the prohibited location until it is potentially discarded later.