I thought logic would indicate a place based on the Middle East would have a Swedish accent.

Does Southlander sound like Texan, Cajun, or Alabaman?

This is why you don’t allow homebrew from idiots.

While amusing, this is either made up as a joke or the DM was really into the idea and willing to overlook a bunch of common sense details (or provide some sort of magic items to compensate).

I’ll grant that the halfling rogue could be breathing through a straw sticking just through the concubine’s sphincter like a snorkel.

That being said, unless she’s decidedly on the chonky side there’s still a person about four to five times the size of a human newborn occupying her lower torso and this should be outwardly visible. A better thought out way to avoid this (which someone seriously pitching it absolutely would think of) is to first shove a small bag of holding up the concubine’s butt and have the rogue climb into that.

Then if the game isn’t a one shot that takes place over the course of a single day the concubine is going to have to either come out for food and water unless she’s shoving those up there not to mention relieving themself. Possibly justify that by having the rogue come out for a snack when she goes off to privately relieve herself or bathe or something, but you’re still left explaining why she’s taking a sandwich with her to go take a dump.

Then the ability doesn’t say anything about instantly climbing into the sphincter of an unwilling person, even if they’re caught by surprise. It also specifically notes that checks would still need to be made to get into such spaces. I don’t see any reasonable interpretation of it (even accepting the inherent fantastical absurdity to begin with) that doesn’t give the victim some sort of saving throw or opposed check to prevent the 30-50 pound humanoid from getting up in there.

Then there’s the matter of “whirling dervish” attacks from within a constricted space. This is actually probably the least issue, mechanically speaking, as IIRC 3.5 rules do allow for melee attacks with light weapons while swallowed by a larger creature (which would be appropriate rules to use even if they went in the other end) and while I can’t recall if sneak attack damage still applies in such cases it would be kind of hard to not hit something vital so sure. And I suppose at that point a dramatic gory torso burst would be an appropriate description of the result.

Still it would just make more sense to hit the naked villain from behind with a regular sneak attack for the same amount of damage without having to justify burrowing into his colon. Or just rule him as a helpless target and use the rules for a coup de grace which grants an automatic critical. Or even more simply go full cutscene and deliver an assassin’s death blow by burying a dagger into his brainstem or something.

Also, per the ability the minimum diameter for a small character (such as a halfling) to fit through is 1" and not 2." Doesn’t really make a difference but it’s the kind of detail that most people giving serious thought to actually carrying out such a scheme wouldn’t miss. Because I’ve dealt with players arguing for some ridiculous things and they always come armed with as many rules based arguments that they can possibly cite. Heck, I’ve been the one trying to convince the DM of some goofy shit on multiple occasions. I never tried this one, but if I did you can bet your ass I’d be pointing out that my character only needs an opening a single inch wide to squeeze through.

Despite the rant I do think it was a funny story. I just like to nitpick.

The DM allowed the NPC to be seduced. It’s been said a million times but clearly that DM hasn’t figured it out yet, the Persuasion skill is not mind control. Tell the bard “she just isn’t interested and your continued attempts to woo her are just making the poor woman despise you more and more every time. In fact, you think you might have heard her muttering something under her breath about taking her chances with the big guy in the spiky black armor. Roll perception. She appears to have slipped away while you weren’t looking.”

If the bard decided to force himself on the girl that would open a whole can of worms but even if the table is okay with such behavior you’ve now pissed off the girl, the local lord, and the BBEG who (as others have noted) could probably find another suitable subject for his ritual with a modicum of effort. After he finishes beating the crap out of the bard.

The payoff was funny but I really don’t think it was worth a year of abrasive annoyance. If the secret paladin and the DM had just been up front from the beginning and made it obvious that the others were getting healed, feeling inspired, etc so that the other players could figure out what was going on sooner it still would have been funny and everybody else wouldn’t have spent a year of gaming pissed off.

This is where restrictive definitions of metagaming detract from the fun of the game. Insisting that “your characters don’t know he’s really a paladin so the DM shouldn’t even bother telling you what the effects he’s buffing/healing you with are” is just BS. Maybe draw out the irritation for most of one session for the sake of a punchline but after that simply knowing that the guy is roleplaying as an abrasive ass rather than actually being an abrasive ass would allow most players to actually enjoy the experience and play along rather than getting constantly ticked off.

There’s also the matter of the PCs, completely in character, not noticing that they’re being healed or being emotionally bolstered against fear. Maybe once or twice in the heat of battle, but eventually there should be cases of “I just know I took a gash in my side there, I can see blood on my clothing, but the wound is closed.” Presumably characters who live in a world where paladins exist would at least know what paladins are and some of what they can do even if they don’t have previous direct personal experience with them. To insist that players should pretend their characters are ignorant is like telling them they aren’t allowed to ask the person in robes and a pointy hat with an ornate staff and an extremely emotive and capable cat following them around if they can cast fireball because they aren’t a wizard, haven’t met any wizards, and clearly have never heard stories of people matching this person’s description making things explode by pointing at them.

Metagaming is, by it’s simplest definition, any behavior that involves acknowledging that you are playing a game. Pretending that fundamental mechanics (like healing or giving advantage against fear saves) don’t exists is just an unnecessary hassle that overcomplicates things and encourages confusion. When you have to stop and think about how to describe something without using game terms, like “I feel as if two more hits like that last one could incapacitate me” rather than just saying “Crap, I’m down to 15 hp,” that breaks immersion for the sake of…not breaking immersion. The PCs should have had plenty of chances to realize what the paladin was doing, and figuring that out much earlier would have made the game a lot more fun for everybody for a long time.