It wasn't long before Yahru returned. He smiled (a somewhat creepy thing, his head being shaped like an anaconda's) and said, Ras Nsi will ssee you. We musst take you by the river, and we only have two boatss. I will pressent you. Ussal and Yasssah will row. Thiss leaves room for three. Five if you inssisst to come, but the boatss will be low in the water. The resst of you musst remain behind."
Yassah is one of the malisons under Ussal's command. Imogen, Dellrak, Myrral, and Chrysagon should go, I suppose. Any objections?
Detect Portal (1/R): Within 1 mile Planar Warrior: As a bonus action, choose one creature you can see within 30 feet of you. The next time you hit that creature on this turn with a weapon attack, all damage dealt by the attack becomes force damage, and the creature takes an extra 1d8 force damage from the attack. When you reach 11th level in this class, the extra damage increases to 2d8. Primeval Awareness (action and spell slot): For one minute per level of spell slot, detect within 1 mile (6 in favored terrain) aberrations, celestials, dragons, elementals, fey, fiends, and undead. This feature doesn’t reveal the creatures’ location or number.
With Imogen, Myrral, and Dellrack and Yassah in one boat, and Chrysagon and Ussal in the other, Yahru took one of the twisted yuan-ti broodguards and settled into the bow of the second boat. At first the strange creature seemed agitated, but the calm Yahru wrapped an arm around its lumpy shoulders and the thing calmed down.
Ussal and Yassah shoved the boats out with their oars and began to row into the dark underground river. It was slow going, with overloaded boats against the slow-moving current, but it wasn't terribly far. As they rounded a bend in the river, on the left, a pebble-strewn bank rose to a door recessed into the cavern wall.
On the right, the river wound around a natural pillar. The banks of the pillar was littered with skeletons. Ussal knew what would happen here, and he hated it. But there was nothing that could be done, and life in the Fane of the Night Serpent was a hard one and he had not survived as long as he had by being overly sentimental. As they passed the door, Yahru suddenly pushed the broodguard overboard. The creature hissed, squeaked, and thrashed about in the water (a surprisingly poor swimmer).
Then something very large moved under the boats and the broodguard was suddenly pulled under. Ussal and Yassah pulled their oars hard, moving as quickly as they could upriver and away. Suddenly the broodguard reappeared above the water, lifted by a large serpentine head. Four more heads burst the surface, spraying water on the slower boat, which threatened to capsize. The serpent heads fought over the unfortunate yuan-ti until the twisted thing was torn to shreds, and then the Hydra settled back into the river as the boats hurried away upriver, leaving the door and the pillar behind.
Miss Imogen saw the serpentine head emerge closest to her ship.
Back at School Miss Enna had taught them not to stand up in boats this small, and she knew it was inherently risky. She was also desperately low on arrows, she felt. Instead, she took advantage of the water she saw slicking of the ophidian's scales, and pulled her fist together, as frost began to form around its jowls.
Cast Frostbite against one of them. Con save vs. DC 12 or 2d6 cold damage (and disadvantage on next weapon attack (? = natural weapons)
As the temperature began to drop in the water-logged boat, frost began to form around Miss Imogen's tightened fist. Yassah, who was facing her while rowing, hissed in broken common, "Do not anger Hydra! Ssshe will kill usss all! Let her eat and sssink away."
Sure enough, as Imogen held back the full force of her magic, the boats pulled away, and the Hydra slipped back below the water.
Chrysagon was surprised by the cruel treatment of the guard, who must have known what was coming. He prayed that Kelemvor took the guards' soul by the hand and lead it to the proper afterlife.
Chrysagon turned his head and asked Ussal curiously; What is behind that door? It is a strange place for a door with such a beast right outside of it, don't you think?