If I use my irresistable faefolk to pull an enemy to an unoccupied battlefield, who is attacker and who is defender?

When you move Irresistible Faefolk to an unoccupied (uncontrolled) battlefield and use its ability to move an enemy unit to that same battlefield, you are the attacker and the enemy unit is the defender.

According to Rule 459.2.b.1 and consistent RiftJudge FAQs (such as #9714, #9828, and #10101), the determination of attacker and defender is based on which player applied the "Contested" status to the battlefield first.

The sequence of events:

1. Move: You move Irresistible Faefolk to an unoccupied battlefield. By doing so, you are the player who applies the "Contested" status to that battlefield. This gives you the attacker designation.
2. Trigger: Irresistible Faefolk's ability ("When I move to a battlefield...") triggers and is placed on the chain.
3. Resolution: When the ability resolves, you choose an enemy unit and move it to that same battlefield.
4. Combat: Because units from opposing players are now present at a contested battlefield, the showdown transitions into a Combat Showdown.

Even though your ability was the mechanic that moved the enemy unit into the combat, you remain the attacker because you were the player who initiated the combat by applying the "Contested" status to the battlefield first.