Potion, Rare
This viscous, putrid oil appears to be slowly etching the glass of its bottle. When poured out it smells strongly of rot.
When this oil is poured onto the ground it transforms an area no smaller than a 10-foot diameter and no larger than a 30-foot diameter into a bubbling sludge. This area is difficult terrain and persists for 10 minutes before drying up. As a Bonus Action you can touch the sludge and cause a Festering Spawn to rise from any point in the area of the sludge (see statblock below). The creature is an ally to you and your allies. In combat, it shares your Initiative count, but it takes its turn immediately after yours. It obeys your verbal commands (no action required by you). If you don't issue any, it takes the Dodge action and uses its movement to avoid danger. It dissolves into nothing when it falls to 0 HP. Once 3 Festering Spawn have risen from the sludge it dries up and the difficult terrain effect ends (though any Spawn persist until destroyed or the 10 minute duration passes).