Although this was just Otto's speculation, in fact, what the Master of Shadows thought was quite similar.
Their plan was simple, since they had failed multiple times to defeat Otto in the real world, they decided to try their luck here.
After all, it was basically confirmed that Otto was a Variant Dragon, so his soul should not be able to reach the same level of strength as his physical body.
So, in the original plan, they just needed to lure Otto here, and the Mother of Evil Dragons could easily bully him.
As long as they exhausted all of Otto's Soul Power here, his powerful dragon body would be theirs.
Even if Otto's soul was troublesome, the Master of Shadows would act as a backup to assist the Mother of Evil Dragons in attacking.
The actual result was like what happened before, it seemed to work at first, but then...