Does the Fathomless’ Tentacle deal extra damage from the Spirit Shroud spell as it is you doing the attack via the tentacle? If so does the target have to be within 10 feet of both the warlock and the tentacle?
Tentacle of the Deeps: As a bonus action, you create a 10-foot-long tentacle at a point you can see within 60 feet of you. When you create the tentacle, you can make a melee spell attack against one creature within 10 feet of it. On a hit, the target takes ld8 cold damage, and its speed is reduced by 10 feet until the start of your next turn. — Tashas p.72
Spirit Shroud: Until the spell ends, any attack you make deals ld8 extra damage when you hit a creature within 10 feet of you. — Tashas p.108