If I attack and my opponent uses Ride the Wind on Ravenbloom Conservatory, do I or the opponent activate the battlefield?

To answer your question: Neither you nor your opponent activates the Ravenbloom Conservatory ability in this scenario.

Here is the breakdown of why, based on the rules of Riftbound:

1. The "You" in Battlefield Abilities

According to Rule 184.6.c:

"‘You’ in a battlefield’s abilities refers to the battlefield’s Controller... If the battlefield has no Controller, ‘you’ refers to no one, and all such instructions are ignored."

Furthermore, FAQ #5361 clarifies:

"‘You’ in a trigger condition refers to the controller of the battlefield and requires control of the battlefield. Only the controller can use such abilities during a contest."

2. Who Controls the Battlefield?

When you move a unit to an empty battlefield, you apply the Contested status. According to Rule 184.4.c, a player loses control of a battlefield if they have no units there, unless it is contested.

If the battlefield was previously uncontrolled (no one had units there), it remains uncontrolled while it is contested. Because neither you nor your opponent has established control of the battlefield yet, there is no "Controller" for the battlefield. Therefore, the "you" in the Ravenbloom Conservatory's ability ("When you defend here...") does not refer to either player.

3. Why the Ability Does Not Trigger

• You are the Attacker: You applied the Contested status to the battlefield.
• Your Opponent is the Defender: They are the one defending, but they do not control the battlefield.
• The Trigger Condition: The ability requires the controller of the battlefield to be the one defending. Since there is no controller, the condition "When you defend here" cannot be met by either player.

Summary: Because the battlefield is uncontrolled, the ability on Ravenbloom Conservatory is effectively dormant. Neither you (the attacker) nor your opponent (the defender) can trigger or activate it.