Gregory calmly observes the beast, now secure in the knowledge that it could not break through the barrier for its duration. Another minute, certainly. Maybe a little longer.

He frowns as he realizes the creature is not created by magic. With a shake of his head, he begins casting another spell, this one to call creatures to his aid. He attempts to summon several lantern archons. Whether there is only one or several, he instructs one to teleport to the Cathedral and to request reinforcements at the St. Abaidas Bridge, by the order of Inquisitor Gregory du Vay, and to give a description of the monster he is currently facing. Any remaining ones, if any, he instructs to distract the beast, not to come within its reach, but hover just out of reach and take shots at it.

He then sets out to cure his wounds and prepare to take down the beast.

Spoiler: Mechanics
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Gregory casts summon monster V, to summon 1d3 lantern archons from the 4th-level list. Once that is done, he gives the instructions, then intends to spend the remaining rounds within his sanctuary as follows: convert restoration to cure critical wounds, convert holy sword to cure critical wounds, and casting detect thoughts to try and glean anything from the beast's mind. Then he casts extended holy sword. After that, he will break the sanctuary by attacking it with a destruction spell. Of course if the creature runs off, he doesn't go through with the rest.

Summons: (1d3)[2]

Not sure these will be relevant, but might as well include them:

Cure critical wounds: 1st: (4d8+13)[32]; 2nd: (4d8+13)[31]
Destruction damage (if the creature succeeds on its Fort save against DC 26): (10d6)[41]

HP (prior to healing): 66/196