what if this episode is where mohn is returned home or poipole return
I do think this is most definitely relating to Guzzlord more than anything for a couple of reasons:
1. The next title is likely Ash vs Kukui (if Ash beat Gladion) and its a full battle. Ash has more reasons to actually have a full battle than Gladion (while Gladion would have to magically produce two Pokemon out of nowhere). So the title should imply what Ash's hypothetical sixth Pokemon, if Ash wins (and I don't be expressly revealing who that sixth Pokemon is, because it could easily be Solgaleo Returns! Which could imply Poipole coming back as well.
2. Mohn could appear, but I don't think it would make much sense considering this is a one off episode, and would be airing right before the full battle. Having Mohn appear in a one off episode, even if its connected to Guzzlord would be a very disjointed conclusion since I doubt they'd throw in Magearna as well, and I think that would be required to find Mohn, is Lillie having Magearna.
3. While Guzzlord could be a one episode deal, I don't know how much sense it makes to have Guzzlord only be one episode, given how serious it seems to be. I mean one could make the argument, that Sun and Moon is really good at making two parters, and while most Ultra Beasts only got one, an alternate Guzzlord did already get two, I just don't think they can cram a good story in only one episode, since while Ash knows Guzzlord is a threat, the other trainer would likely need to see it, hence I do think suspense needs to be built for most of an episode, to carry over the next episode, to make a proper conclusion. Otherwise its just weird.
Other possibilities-
1. Could it be relating to 8th generation anime? Maybe, the announcement apparently happens at this episode, but having a disjointed episode, just to have 8th generation anime being the focal point of the episode, or having it relate to the title could be weird.
2. Could this be a battle between Masked Royal and the winner of the league? It would have to be a build up episode, at best like the Battle Frontier episode where Ash calls back his first Pokemon (that he still has access to), but making that a full episode. I have doubts that this episode would be the start of the battle if only because I don't know if the way the title is presented it would apply to a second parter. Like would a second parter of a full battle simply just have "A Full Battle" or would the title more imply that it is the 2nd episode of the full battle? But the point being could this episode be primarily about getting ready for the full battle, sure, giving Ash a chance to get his 6th Pokemon.
3. Could an evolution be revealed in the title? Possibly, maybe Torracat evolves in this episode, and that would likely confirm even more that Ash is going to battle Masked Royal. Because why evolve Torracat only for it not immediately be used in the previous episode, though if Torracat will ever evolve, I think its going to evolve during the battle like how Litten evolved, not to be a DEM and why Ash might beat Masked Royal but just a call back to their first episode where Litten evolved into Torracat.