We fought the last battle today and defeated the big bad - a beholder many-eyed watcher! It was a brutal battle, even though we took in 15 PCs worth over 400 points. By the end, we had 2 dead PCs, 2 unconscious and all the rest but 2 wounded, most at 2 of their 3 HP.
The scenario as written has a flame curtain and a metal chain wall that pops up and crosses the whole board. Given I lack the right terrain, I had the flame curtain cover the entrance where the tiles turn to hellscape. It required a DL 12 Will save to cross (in RoSD it does one damage, but I removed that as HP are much less common in Sellswords). This trapped several PCs for many turns. On the table, you can see the small red squares - those represent the flame curtain (I ran out of time to do something with hot glue).
For the chain wall, that was represented by the white squares and surrounded the tower where the many-eyed watcher and his bodyguard (a Chaos Champion) were. Removing the chain required climbing (DL 14) and then cutting the chain at the ceiling. Three PCs successfully climbed, but then two fell, meaning they both suffered 2 HP damage from falling 8" - this put both OOA and ended up killing one. That PC ended up hanging on the chain wall directly in front of the many-eyed watcher, so we ruled he freaked out and let go. The 3rd, my floating spellcaster Peldoss, managing to cut the chain and float down without taking damage, but ended up right next to several temple guardians (the snakemen) who were leashed to remain within 6" of their pillar (the purple uprights with gold writing). This ended up being a last stand for them, as the guardians took them down.
The many-eyed watcher was a nasty beast - it has 6 HP and is DL 17, which is hard. We ended up having them just use the various scenario-written events (coming up on the Scenario Event and Complication cards), but when those ran out, then they activated as per normal. 3 attacks per activation, each targeting a random PC within their line of sight, which given their height, was everybody. Brian's Ser Fluffels - the cat mage, ended up losing some hair but not much else because Brian rolled disintegration beam and the PC had zero equipment.
Speaking of magic, we had the worst luck with Mana Flux. On a roll of 1 or 2, this adds a -2 (cumulative to -4) to all magic rolls. Between the three of us, I think we rolled 5 or 6 1s, so the magic was nearly permanently at -4. It rose to -2 very briefly. This mean basically zero magic got off - two fireballs from Ser Fluffles and nothing from Peldoss.
So what killed the Many Eyed Watcher in the end? Mostly the three halfling archers, all badly wounded but standing bravely firing arrow after arrow into first the bodyguard and then the many-eyed watcher (including a pair of 20s!). Not bad for being the cheapest PCs on the table (all three were only Archer 2, with no armour and other stats).
Finally, I'll write up a full conversion guide on Warbard soonish. You'll need to buy the adventure, but I can write down what I changed to make it work in Sellswords.