Ir Yut would dominate the Gatekeeper. The Gatekeeper is very slow, despite its teleportation, while Ir Yut is quite agile. Also, Ir Yut, as she always does, can run off to a secure location and begin the Liturgy of Ruin. Unless the Gatekeeper, being extremely slow, can find her AND kill her within 30 seconds all by himself, he's screwed.
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1. This is a battle strictly between Ir Yut and the Gatekeeper, there are no minions involved. 2. You are assuming that the Gatekeeper will know exactly where she is, all the time. As previously stated, she can just run off and hide while she does it.
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Here lies the problem; we don't know if the room in which they are battling is a flat landscape, or a room filled with complex obstacles. In my opinion, that would dictate the outcome of the battle. Also, keep in mind that the Gatekeeper fires in short bursts, and doesn't fire all the time. In fact, he commonly just floats there and doesn't really do anything other than teleport around. He only fires a burst or two every now and then.