So, this is not exactly an adventure hook, but rather a little story about how we included Ravenloft in our Dragonlance setting back in the good old days. Hopefully, somebody can find some inspiration from this post, or at least be a little entertained.
The whole story started with the Tower of High Sorcery of Istar. In our campaign the tower was transported to the demi plane of dread, Ravenloft, shortly before the Cataclysm struck Istar. My DM got the story hook from one of the Dragonlance comic books.
My black robed wizard found out that the tower wasn’t destroyed in Cataclysm, and after many dangerous adventures, he was able to locate it in Ravenloft. Hen entered the tower, and basically had to pass his Test of High Sorcery again. Long story short, he passed the Test and became the Master of the Tower.
The Tower still included the original portal to the Abyss, but since the Tower was located on a different plane, and since there was no white robed cleric around, the Portal opened up in Scull Cap back on Krynn. This little nifty trick allowed us to run a campaign that spanned across the Dragonlance and the Ravenloft setting.
Shortly after I more-or-less retired my character since he had attained level 23 or something like that. The character was used as a high level NPC, who could help the party travel between planes.