It shouldn't work.
Even if the PC had the means to telepathically communicate (bearing in mind only the Aboleth has telepathy and can stop listening at any time shutting the PC out from responding) the Aboleth needs to hear and understand the PC.
Hear being the operative word.
You don't 'hear' telepathy any more thsn you hear sign language, even if you understand what is being communicated in both forms of communication.
Part of the text of Suggestion states "If the suggested activity can be completed in a shorter time, the spell ends when the subject finishes what it was asked to do."
What does "naughty word off" mean in terms of the spell? Leave the vicinity? Travel as far away as you can? Don't bother us?
I'd be tempted as a DM to have the aboleth "naughty word off" until it can't sense the PC anymore, at which point the Suggestion has been fulfilled and its free to come back.
Sure but F off is more memorable. Travel 100 miles north would have also been sufficient.
being a pedantic prick about suggestions just isn’t any Fun.
The "Hear and Understand" portion of the spell heavily implies that the suggestion is verbal, not telepathic. I'd rule against it working.Yeah, but those are two separate requirements. It can hear the caster because they're standing within 30 feet of it, and it can understand them because they're in telepathic communication with it.
And sure, it could relinquish that communication, but from its viewpoint, why would it do so? It's not going to know it's in trouble within the time it takes to mentally project two monosyllabic words.
The "Hear and Understand" portion of the spell heavily implies that the suggestion is verbal, not telepathic. I'd rule against it working.
I can see it going either way and wouldn't complain if a DM ruled it worked, or if he ruled that it didn't. To me, the suggestion is a part of the spell and would be verbal. Spells don't really shift to become telepathic if they are verbal. The spell doesn't explicitly say that, though.Well it is verbal in the ordinary sense. The question is whether you are able to hear and understand a telepathic comminication. Id say you are able to do so because 5e is written in natural language and those words are exactly what I would use to talk about telepathic communication in natural language.
Would a creature really find it "reasonable" to travel 100 miles north for no reason? I'd think a valid Suggestion should include a reason why the affected creature would want to do such a thing.
Suggestion is a 2nd-level spell with frustratingly vague rules for how it works. Based on how the DM rules "reasonable" it can be nearly useless or the best mind manipulation spell behind Mass Suggestion.
I've been planning a yuan-ti focused campaign for a while, and even the CR 1 yuan-ti pureblood has Suggestion as an innate spellcasting choice three times per day. I really just want to use yuan-ti because snakes are cool, but I can't let their Suggestion ability go unused. I've got to figure out how I think this vaguely defined spell that could be potentially used against the PCs in that campaign very often should work. I don't want the yuan-ti to be able to just compel the PCs to naughty word off constantly, for example, so I need to hammer out a more precise and consistent ruling for how Suggestion works than 5E's designers did (the given example of a knight giving away their horse doesn't sound that "reasonable" to me, honestly). I think one of the solutions there is to be pedantic about how the supernatural suggestions are worded. I also don't want to neuter Suggestion to the point that it's basically just an alternative to a Persuasion check, though.