The PCs continued along the desolate land within the Astral Sea, toward the headquarters of the Ilun Sembre as the map indicated.
As they travelled, the PCs noticed stranger and stranger things happening. Their minds were starting to fray, and out of the corner of their eyes strange shapes and creatures would appear and disappear at random. It got worse as they went closer to their destination. Reality itself seemed to be dissolving.
The PCs crested a small hill and found themselves overlooking a strange scene. There was a giant gateway on a pedestal in the middle of the featureless plain. The gateway was made of a strange metal alloy that seemed to flow constantly with different hues. Despite the flowing metal, there were strange runes and symbols carved into the gate that did not flow. The symbols and runes, to those trained in magic, were almost offensive: they bespoke a completely different approach to magic that would not work in this reality.
In the middle of the gate was a portal swirling with green energy. There was a gigantic sphere floating above the pedestal in front of the gate. The sphere was decorated all over its surface with large eyes that were currently closed. The sphere swirled with the same green energy which was flowing out of the gate and directly into it.
On either side of the gate, hastily set up on the ground, were a few tents. There were a couple forsaken and some overly large illithids milling about around the tents, and one of the forsaken yelled toward the PCs as they approached. He taunted them, telling them that it was too late to stop the summoning of Allabar, Opener of the Way, and that their reality was doomed.
The PCs did not give up, and dove into battle with the last of the Ilun Sembre. They came out of the battle unscathed, though they did not have much time to rest. Only a few moments after the last of their foes were slain, all of the eyes on the sphere simultaneously opened, and the sphere moved toward the PCs.
Allabar was a challenging foe, a dark god that had been banished to the Far Realm and twisted by its strange reality. The PCs fought with everything they had, and bested Allabar, banishing him back to the Far Realm, and reclosing the Gate.