Yes, you can use the tentacle attack and eldritch blast on the same turn
The feature - which is almost exactly the same as the Tentacle of the Deeps feature from the final Fathomless patron detailed in Tasha’s Cauldron of Everything - says:
As a bonus action, you create a 10-foot-long tentacle at a point you can see within 60 feet of you. [...] When you ...
Attacking with the tentacle is always a bonus action.
The ability reads:
When you create the tentacle, you can make a melee spell attack against a creature within 10 feet of it.
So when we create the tentacle, we make a melee spell attack. To create the tentacle:
As a bonus action, you create a 10-foot-long tentacle
So with a bonus action we can create ...
You’re the DM. It’s your world.
It’s totally up to you to determine if such a being is a suitable warlock patron. It’s your world. As the DM, you are responsible for building it.
That said, the guidance in the PHB about fiend patrons says:
Fiends powerful enough to forge a pact include demon lords such as Demogorgon, Orcus, Fraz’Urb-luu, and Baphomet; ...
This is balanced, except possibly if your party regularly takes several short rests per day.
The Dungeon Master's Guide gives guidance for changing spell lists - essentially, it is usually a priori balanced, giving special attention to messing with warlocks:
Modifying a class’s spell list usually has little effect on a character’s power but can change the ...
If nothing else, the tentacle can always attack an empty space (you need to have this ability so that you can make attacks into spaces you think might have a hidden enemy), so even if forced to “attack” there, you could easily choose to avoid having that attack do anything. So I think it’d take a really pedantic DM to make you attack if for some reason you ...
There is no penalty. No writen rule, no mandatory penalty.
This is a roleplaying game. No rules penalties doesn't mean no consecuencies. But, as a player, dire consecuencies are just more challenges to defy, more opportunities for fun.
The class has aligment restriction. That means characters with the correct aligment may take levels in the class (and only ...
Complete Arcane, page 81. I'd give some more details to show that the Warlock is allowed to do this, but the description of Maximize Spell-Like Ability does the work for me - it uses the Warlock as an example:
For example, a 10th-level warlock’s maximized eldritch blast deals 36 points of damage three times per day.
and it also covers Empowering:
An item’s caster level affects how vulnerable it is to being temporarily suppressed by dispel magic and the like.
And unless the item is duplicating a spell effect (e.g. spell-completion, spell-trigger), that’s it.
It isn’t a minimum requirement on crafting the item, it doesn’t affect the power of the item’s effect, it doesn’t interact with feats. It ...
This question is somewhat subjective so instead of answering with a list of spells instead I will suggest some tools.
DnDBeyond let's you search spells by level, by action length, and by whether they have a material cost. You can use this to try and find spells that have large material cost components that you find valuable.
For duration, most sites don't ...
These requirements do not interact, you just need to meet each of them independently.
Unlike the Empower Spell and Maximize Spell feats, the spell-like ability versions don't do anything like change the effective spell level of the ability they modify. Instead, they have two requirements:
You must be able to use a spell-like ability at caster level 6 or ...
The attacks are resolved one at a time
Each beam of eldritch blast involves a separate attack roll and is resolved separately
This is clear from the spell description:
The spell creates more than one beam when you reach higher levels: [...] Make a separate attack roll for each beam.
Thus, we can refer to the section on "Making An Attack":