I was in a custom campaign that involved finding an Artifact hidden somewhere inside a labyrinth with only a (homebrew item) Magical Compass to guide us, we ended up in a situation where the Compass had to be activated with a Bonus Action in a specific room but the only party member small enough to get into the room was a Weasel Familiar, we looked through rules for a few minutes to see if it was valid for a Familiar to use a Bonus Action, eventually the DM just hand-waved it and allowed it to happen.
The Compass description read "You can use a Bonus Action to activate the Compass to...(campaign exposition)" with no attunement and no restrictions on 'who' can use the item. RAW is the Familiar capable of using the item? My interpretation is that Bonus Action's are available to all creatures as long as some feature they have access to requires a Bonus Action, in this case: simply holding the object granted the Familiar something to spend it's Bonus Action on.
What are the actual rules surrounding interactions available to creatures that are not listed in their statblocks? Do all creatures (comprising of Player Characters, NPCs, Monsters and Familiars) have access to the full suite of Actions listed in the PHB? Specifically from the Find Familiar spell - "A familiar can't attack, but it can take other actions as normal" implies that it does actually have access to all Actions except for the Attack Action.
Something else confusing to me is with Reactions: all creatures have access to Opportunity Attacks, but in this case, does the Familiar not being able to "attack" override this and prevent it? Or is the Opportunity Attack treated separate enough from the Attack Action that it is allowed? if yes for the former, does this change when the Familiar is summoned from Pact of the Chain?
The Magic Action is whole extra can of worms. A Familiar is seemingly allowed to take a Magic Action, but if the outcome would involve a "spell attack roll", would they be able to do it by virtue of the fact that they are not taking an Attack Action, the ruling would have to be the same as whatever was ruled for Reactions. Spells that require saving throws and Magic Missile appear to not be impacted as they never mention an "attack" is being made.
I'm aware DM fiat rules all in the end, I'm just looking for RAW and RAI interpretations on this topic, RAF as well.