[...] 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 a creature within 10 feet of it. On a hit, the target takes 1d8 cold or lightning damage (your choice when it takes the damage) and its speed is reduced by 10 feet until the start of your next turn. [...]
As a bonus action on your turn, you can move the tentacle up to 30 feet and repeat the attack.
So you use a bonus action to conjure it, then you can make a melee spell attack - but does this melee spell attack count as an action?
- If not, you can eldritch blast and also attack with the tentacles on the same turn, right?
- And if it does, can you just eldritch blast and then use the second hit as a bonus action?
(I know that that there is now an official version of this warlock patron published as The Fathomless in Tasha's Cauldron of Everything, but I liked this version way better.)