In tonight's game, a player got an encounter where he could choose and remove any card from the Mythos deck. Well we were using every expansion, so it wouldn't really matter, but we still looked for one. Since someone was about to seal a Graveyard gate, we searched for all the Graveyard gate bursts. I believe there were four. They all had somewhat mild Mythos effects:
Citzens Urged to Lock Doors (some monsters added)
Full Moon (all monsters have +1 horror damage)
Local Heiress Missing! (the chances someone would get Asenath Waite as an ally were tiny)
Stalkers in the Night (some monsters removed for a terror increase)
We decided that "Full Moon" was the most damaging, so we removed it.
Flash forward a few turns.
Michael McGlen found himself in Kingsport trying to close a rift. He had the opportunity to add two rift progress tokens for a reward, and opted to do it. The reward was to be joined by Asenath Waite! This caused Michael's personal story to fail, which lost the $10 she came with, and killed his Retainer. He could not take the train home. Good thing, he had a lot more of a rift mess to clean up now.
Anyway, we laughed about how unlikely, but horrible it would be, if our next Mythos card was "Local Heiress Missing!". Well, guess what it was?
Local Heiress Missing! (and yeah, I shuffled)
Michael lost the money Asenath gave him and the money he already had, and his retainer stopped working, stranding him in Kingsport to deal with a rift problem that was twice as bad as when he showed up. Then, his new ally ditched him, adding a doom token on her way out.
Needless to say, we lost that one. But it's okay, because we got some kind of revenge. We played another game, against Azathoth, where we removed a bunch of doom tokens by using an Eltdown Shards, The Messenger, Silas's story, and William Bain (twice!). Interesting note: the character who got William Bain died to a Shan, and her replacement started with Bain and died to the same Shan. Conspiracy?
. I'm surpised the Tendril was so lethal; I'm guessing your group was short on Spells and magical weapons?