CapnZapp
Legend
It's called "exhaustion". If you search for "fatigue" you won't find it.5E has a fatigue system. It's a track. 1-5 (or 6), final stage is death, second to final is "Speed 0". It is only cured by a long rest or a greater restoration spell, so fatigue on something nearly flags it as a "once per day" ability. The first level of fatigue is "disadvantage on ability checks", which can already be painful.
As for the ink, 1 round would make it a minor enough ability. I'd still put a short rest recharge on it. Though I suppose its utility depends on how often the party is underwater.
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