HARMFUL GAY STEREOTYPES EMBODIED BY MOHG
lives in sewer
kidnaps children actually he was cleared of this one
blood magic
never stops being funny
If it had happened before, he would have returned to the Halligtree. The fact that he had power over Mogh and yet stayed shows that it wasn't a kidnapping.
A lot of things kind of happened at the same time, and Miquela is adlibbing, reacting as best he can on the fly to hold together a plan that started actively falling apart the moment his attention was somewhere else.
So yeah, Miquela cocooned himself in the haligtree, and Malenia led the Haligtree's armies South to Caelid to retrieve Radahn. It's not clear why Radahn didn't simply go to the Haligtree himself, since we don't get much first hand characterization of Radahn. Personally I think that Radahn was still on board with the plan, but he knew becoming Elden Lord would require his death, however temporary, and his warrior pride wouldn't accept any death other than a glorious death in battle. This fits with how Freyja talks about him, and with her choice to side with Leda against you even after she's freed from Miquela's influence, provided youve informed her of what Miquela and Radahn are actually trying to do. Note the contrast to Amsbach, who is to Mogh what Freyja is to Radahn, and who sides against Leda once he has the full picture.
Regardless, Miquela embeds himself in the Haligtree, or becomes the seed from which it grows, and Malenia goes to retrieve Radahn, which goes poorly for everyone. Radahn obtains neither victory nor glorious death, and the lands he once protected are completely destroyed. Malenia doesn't kill Radahn and so fails to send him to the Shadow Lands to be reborn as Miquela's consort. Worse, she loses Miquela's golden needle which had kept her rot in check, and by letting the scarlet rot bloom in a last ditch failed attempt to kill Radahn she corrupts his physical body and mind. IMO it's quite likely that the original plan had been to revive Radahn in his own body, and a substitute body only became necessary after Radahn's body was ruined in the battle.
Then Malenia's unconscious body is dragged back to the Haligtree, and when she awakes she learns that not only did she fail in her mission, possibly ruining the entire plan outright with what she did to Radahn, not only did she lose the needle Miquela gave her to keep the rot from consuming her entirely, in her absence Miquela has been abducted, torn out of the Haligtree, arresting its growth and possibly even killing it. Now nobody knows where he is or how to find him. And in her despair, without the needle, she loses control and lets the rot bloom a second time - hence the flower outside her boss room - spreading her rot to the roots of the Haligtree, further ruining the plan. No wonder you find her in a state of catatonic despair.
So then we have Mohg and his Blood Cult devoted to the Formless Mother. Mohg wants to found a new dynasty to claim the birthrigh he was denied by virtue of his Omen curse. But if Mohg is going to make himself the Lord of a new age he needs his own divine spouse. For the sake of the legitimacy of his would-be rule, especially as an Omen, he really needs that spouse to be Miquela, Radagon's favorite and Marika's obvious Heir apparent. So he finds his way to the Haligtree and waits and watches for the moment when its master is undefended, and takes Miquela's body by force while the divine child's mind is away in the Shadow Lands and his sister and her armies are on campaign in Caelid.
I don't think this abduction was 'part of the plan' from the beginning. Again, until Radahn was infected by the scarlet rot, there was no reason why he could not have been reborn within his own body. Malenia's despair fits best with a plan that was, as far as she knew, fully derailed and unsalvageable. Otherwise no reason not to just march back south to try to kill Radahn again in his now much diminished state.
So once Miquela got his fingers in Mohg's brain, why stay with Mohg? Why not just return to the Haligtree? Well, for one the tree is rotted now. If Miquela's cocoon was put back the rot might infect him. Also, whether it was always necessary or whether I'm right and it only became necessary after the fact, Miquela does now need a new physical body to revive his divine consort's spirit into, and Mohg is right there. Using him as a sacrifice would be poetically ironic retribution for abducting Miquela in the first place.
And it's not like the lands between are a particularly safe place these days. Marika might have been on board with this plan at some point, maybe back when her own favorite child Godwyn might have been the chosen lord, but she very much isn't now. And while her personal influence is limited in her current, crucified state, she has called back a hoard of unkillable Tarnished warriors from the lands beyond, possibly including f'ing Godfrey himself, to stalk the lands between murdering any demigod they can find in search of great runes. These tarnished could be a useful tool if Miquela can aim them at the stubbornly unmurdered Radahn, but if any of themt find Miquela himself that could pose a real problem. Maybe he could have Mohg's blood cult look into turning the tarnished against each other?
Beyond that, there's the undead deathblight plague, outbreaks of yellow madness, the scattered remnants of the black knife assassins, Godskin cultist, Rykard's heretics, and Godrick down in Limgrave. Most dangerous of all is the current King of Leyndell, who also might have been on board with the planned succession at some point, but who now considers Miquela and the forces of the Haligtree to be just as treasonous as Volcano Manor. And then there's Ranni, who has at times played the part of an ally in Miquela's plans, but who clearly has her own agenda and is still out there somewhere plotting who knows what. Malenia is in no longer in any condition to defend Miquela from these threats. Without her needle she honestly represents as big a threat as any of the rest. She could lose control and blossom into a deadly rot goddess at any moment, becoming a direct rival to Miquela's own ascension.
So with all that going on, this hidden and largely inaccessible blood cult refuge that Miquela's unexpectedly found himself in is as good a place as any to keep his physical body while his spirit stays in the Shadow Lands preparing for his divine apotheosis. Once he has the power of a god and the strongest and handsomest (non-deathblighted) demigod as his Lord Consort he can return to the Lands Between and start picking up the shattered pieces of his master plan to fix everything bad and make everyone be nice (by force, or else).
Which is all a long way of saying that even though Mohg is definitely under Miquela's influence by the time our Tarnished arrives in the Lands Between, and Miquela seems to have deliberately chosen to stay with Mohg for the time being, it still seems most likely to me that Mohg's initial abduction of Miquela was entirely his own decision, made with the intent of forcing the divine child /heir apparent of the golden order into what is essentially a political marriage to legitimize his new blood-cult dynasty.
So yeah, If you kidnap a child that still counts as kidnapping, even if the child subsequently kidnaps you back and/or decides they'd rather stay with you than go home.
