Flooded Ruin Complications

The rule

Roll on the table when the party first enters a flooded area, every 10 minutes they stay in one, and whenever a fight breaks out waist-deep or deeper. On a result the room has already used, take the next unused number down instead. Complications last until the party leaves the area unless the entry says otherwise. Saving throw DCs assume a party of level 5 to 10; drop them by 2 below that and raise them by 2 above.

Flooded ruin complications d12

d12	Result
1	Silt cloud. Something stirs the bottom and the water goes opaque. Everything below the waterline is heavily obscured for 1 minute.
2	Rotten floor. A flagstone gives way under a random creature, which must succeed on a DC 13 Dexterity saving throw or drop into a flooded chamber 10 feet below.
3	Undertow. A current starts pulling toward the deepest point of the area. Each creature in the water must succeed on a DC 13 Strength saving throw or be moved 10 feet in that direction.
4	Leeches. Each creature that is waist-deep or deeper must succeed on a DC 12 Constitution saving throw or pick up leeches, losing 1d4 hit points every 10 minutes until someone spends an action picking them off.
5	The tide rises. The water climbs 2 feet. Waist-deep areas become swimming depth; dry ledges become ankle-deep.
6	The drowned bell tolls. Every creature in the area must succeed on a DC 13 Wisdom saving throw or be frightened until the end of its next turn. Any undead within 300 feet now knows the party is here.
7	Air pocket gives way. A trapped bubble of foul air bursts to the surface. Each creature within 10 feet of it must succeed on a DC 12 Constitution saving throw or be poisoned for 1 minute.
8	Floating debris. A mass of timber and wreckage drifts through. The area becomes difficult terrain, and anyone fighting in it has half cover from creatures on the far side.
9	Eel nest. The party disturbs a nest of giant eels (use constrictor snake statistics with a swimming speed of 30 feet): one eel per two characters surfaces and attacks.
10	Salt rot. A random character finds one nonmagical item (rope, rations, a spellbook's binding, a map) ruined by seawater.
11	Lights out. A surge of water sweeps through at head height. Every torch and open flame in the area is doused; lanterns survive on a DC 12 Dexterity saving throw by whoever carries them.
12	Drifting pilgrim. The body of a drowned pilgrim bumps against the nearest character. It carries something worth finding: a clue to the way out, a key, or one roll on the area's treasure table.

When to use it

Coastal, sunken and swamp dungeons, sea caves and drowned temples, and any adventure with a tide clock. Works well alongside The Drowned Abbot's Vigil and Before the Tide Turns.

What it costs

Mostly it slows the party down and spends resources: expect one or two extra short-rest-worthy hits of damage across a flooded dungeon. The eel nest (9) is a real fight at low levels; swap it for the leeches if the party is below level 3. Nothing here scales with the party beyond the DC note, so at level 11+ treat it as flavour. It punishes parties who rely on torches, which is the point.