Ilbranteloth
Explorer
In addition, it doesn't take an action to share senses unlike with the base spell, .
Where do you see this notation? I don't see anything in the warlock that says you don't have to use an action to communicate.
If you're referring to the variant description in the MM under each creature, I would say that those abilities apply only when the creature in question is choosing to serve as your familiar, because it's actually an imp, quasit, or pseudodragon that is serving you, rather than a celestial, fey, or fiend spirit that is only taking its form as described in the warlock ability and find familiar spell.
To be clear, there are only a few things that differ in Pact of the Chain from just casting find familiar, at least as written:
1. It doesn't count against your number of spells
2. You can choose a special form for your familiar
3. You can forgo one of your attacks to have your familiar make an attack instead
That's it. You don't get an actual imp, quasit, pseudodragon, or sprite to serve you. They can communicate telepathically, but only within the limits of the find familiar spell. You don't get the extra benefits of the MM variant if you're not allowing the creature the ability to end the servitude at will.
You don't gain magic resistance, and I'm not even sure if the familiar would have abilities like shapechanger and invisibility. Although I wouldn't outright disallow these, we'd decide as a group, but having an at-will invisible spy at 3rd level without having to cast a spell is fairly powerful.
The reality is, that there's a lot of room for interpretation in the rules, and as a long-time player and DM I'd be fine with whichever variation has already been floated in this thread. But I think the currently written rules are fairly clear with the exception of what actual abilities a familiar in the 'form of an imp, pseudodragon or quasit' actually has.
Ilbranteloth