by CHUNIA
With regards to adds - the initial wave was mostly cleared with Angel of Death (Eclipse level 9 card) top on the first turn. The setup was:Starting positions - Eclipse top right, Diviner bottom right.
Diviner goes first (among characters), with Trackers attacking beforehand. Seal Their Fate bottom (move 3 attack boss) towards the Eclipse, Planar Fissure top dropping the rift near the boss. Ring of Haste into Call of the Nether (changing places with the bottom Tracker). Rift Device (item) teleport 4 hexes up (into the lava, ouch), Ring of Brutality into Otherwordly Journey to teleport the remaining Tracker adjacent to Eclipse, create Dark with the wand. Savage and Scout move to attack Eclipse on their own, as he is their focus due to distance. Eclipse goes at late initiative, killing the 4 of them (2 Trackers, Savage, Scout). That leaves just the Ashblade, whom we pretty much ignored, plus the occasional additional summons (think we only got 1 additional Tracker on the successful attempt). This setup eats a lot of damage on turn 1, but shouldn't get hit following that.
The routine for the remainder of the scenario -
Diviner - teleporting in and out of the walled off spaces, at early and late initiatives respectively (think I used cards with 75 and 91 for "late" and 08 and 13 for "early"), and does the melee attack 4 (using Balanced Blade). On turns 5 and 10 using Ring of Duality and Second Chance Ring (renewed for turn 10 with Pendant of Dark Pacts) to Put Tokens -> (Ring of Duality) teleport -> Move 3 attack -> (Second Chance Ring) -> teleport -> put tokens. This minimizes the total healing the boss receives.
Eclipse - build the hand for maximum damage (instead of Kills) - using Lurking Ruin + Empowering Void for Attack 10's, Silent Force top (+Night Blade when not directly consuming Dark with cards) + Quiet Frenzy bottom for Attacks 7+3, etc. All while staying invisible with Cloak, Smoke Elixir, and returning combos with Stamina Potions and Star Earring (we actually used the official nerf - -1 card returned on each item - for the whole campaign).
Both characters ran Boots of Quickness (+Star Earrings) to help manipulate initiative and maintain the tactics above. I can provide full item loadouts if you're interested, but both characters were optimised to the maximum for the task at hand. Only short rests were used to waste no turns. Both donated to get 2 additional blesses.
Biggest issues (requiring multiple repeats) came from boss abilities: main offenders being
a) Taking control of the character - not much to do except make sure Eclipse had higher initiative than the Diviner on turns 5 and 10, to avoid the mass summon
b) The heal/shield card - thankfully we only got it once on the successful attempt
c) The trap creating bottom - avoided by Eclipse by staying in melee range, and by Diviner using the rift dropped on turn 1 (spaces with rifts are not considered empty).
Even with the strategy above, success is still RNG dependent due to random nature of Boss actions - mainly how many turns you waste due to Boss taking control of characters, but it is doable. That's why I'm genuinely wondering which classes can complete it on 2p, apart from the 3 burst ones I mentioned.
This kinda reminded me of "superbosses" from JRPG's - hope there's place for such scenarios in Frosthaven, although they probably are better off being optional.