I see nothing about casting necro dots/taps here.
"Tentacle Terrors are found in both Najena and Unrest. The Terrors in Unrest are level 25+, while the ones in Najena are level 17 to 22.
The whip is a very rare drop from them, the terror spines are slightly more common.
Tentacle Terrors have an interesting "blowback" effect sometimes, which can make fighting them annoying. It's very inadvisable to have your back to a zone line while meleeing them, as you may inadvertantly zone."
They'd likely have a pet if they had necromancer spells.