I need to brag, briefly: I finally finished Vicious Gaan-Talet, so now maybe my mind can rest!
I played a Dwarf Rogue, prepping the Tri-Sword and worshipping only Dracul. This dungeon clearly calls for a huge amount of longevity and Dracul really provides that, between 15% resists, Sanguine (I think I had 5 ranks of it!) and life steal (only 2 ranks, because it comes with the max resistance penalty.) Sanguine is just huge; I can't imagine doing the dungeon with anything but a Dracul follower or bloodmage. And the Dwarf race helps maximize the impact of bloodpools. The Tri-Sword, by contrast, didn't really explode; I spent too much money on a Troll Heart (although I don't regret the bonus health) and some potions for killing some problematic mini-bosses.
* Translocated a Platemail very near the end. This was a huge help; between the Platemail and 20% resists, my health really went a long way against Horatio.
* I don't much like the Martyr Wraps, but those seem like they would be quite helpful; likewise, a Piercing Wand would help deal a lot more damage to Horatio.
* The 3-curses penalty turned up on Horatio's level! Luckily, I had saved four popcorn monsters.
* GETINDARE was helpful of course, but it didn't seem as critical as it has in other Vicious runs.
* You need to keep your fingers crossed that Dracul when you need him (early!) and that the level penalties don't line up in a bad way, like the "full reveal" penalty on the large level, or Retaliate Fireball on a level with physical resist monsters. On the other hand, you can get unexpected benefits--like the No XP level happening on a level with a No XP bonus enemy, or the Poison/Manaburn penalty happening when you were just about to ding anyway.
If there's a way to beat this level that doesn't involve copious blood-drinking, I'm very curious to hear about it.