We played last night, first time with both Dunwich and Kingsport add-ons. The Ancient One was Yibb-Tstll (sp?) and all I can say is he was TOUGH! The fact that you couldn't have more than 5 Clue Tokens was challenging enough, but due to an errant Rift opening up, he woke up pretty soon. His skill modifier is -X, where X is the number of Clue Tokens left on the board. We weren't sure if that meant just the Arkham board, or also the Kingsport and Dunwich boards. To give us something of a fighting chance, we decided just the Arkham boards (there were only 2 Clue tokens there, but 4 in Dunwich and 1 in Kingsport, at a minus SEVEN, that effectively took two of the four players out of the fight, so we said let's just do -2 and have something of a fight).
However, even at only -2, because he was "double the needed successes to remove a Doom Token", he was impossible to kill. We needed EIGHT success (times 11) to kill him. Two characters died after the first round, the other two were able to knock off two Doom tokens. The third player survived and was even Blessed, but didn't help since the next roudn he died. The exact same thing happened to the fourth player, survived and was Blessed, but the blessing didn't help and he only lasted one more round.
Anyways, just so's ya know, Yibb is one tough cookie. Don't let him wake up
P.S. Combining the two add-ons wasn't as bad as we thought, mainly because the Mythos deck is sooooo diluted now, the Dunwich Horror never got close to waking up (though Monster Surges sucked for that reason). Kingsport Horror though was VERY nicely done, since the "danger" there is not dependant on Kingsport Horror Mythos Cards (unlike Dunwich), so we had to early on send an Investigator up there to keep the rifts in check.