Six months later, we're starting the Champion's Belt, so (of course) I've got more conversion questions...
1) There's no conversion for Loris Raknian or Okoral. I'm thinking Warlord from Volo's (CR13) and maybe Assassin. And give them some items.
2) Page numbers are missing in the "Raknian's Security" section of the conversion notes (there ## placeholders)
3) For the gladiators, you didn't include all the magic armor/weapons. eg. Rennida has a "frost longbow" (presumably does d6 of frost damage on a hit). Left out on purpose? It's an excellent opportunity to have magic items because the players don't get them after the battle! But maybe because it's not an official 5e weapon it's better to leave it out?
4) You left out "Scriminaduro", the dire badger companion of Joren that "rages" after it's hit and has "Magic Fang" (?) cast on it. There are no dire badgers in 5e so I'm at a loss!
5) I might have added the land-based equivalent to the Peryton's "Flyby" ability for the mounted Korush warriors. This allows them to ride by without provoking an opportunity attack and matches their skills in the original.
6) The two gnolls with Joren (his "Halberdiers") - it feels like Gnoll Pack Lord or even a Gnoll Fang of Yeenoghu could be used for them?
Had the first battle last night.
The biggest issue was the 100' between each starting team. The PCs cast Fireball repeatedly and decimated everyone else. The melee enemies slowly run across the field and get destroyed by conjured/summoned creatures as Fireballs and range weapons hit them.
The archers were deadly, but not for the spells. Rennida get +10 to hit, 3 attacks a round, 150' range for d8 + 5. That was a lot scarier than Magic Missile or Melf's Acid Arrow.
I used Dire Wolf for the badger, but it failed its save on the first Fireball and died without an action. I used two Gnoll Fangs but they move 30' and have only melee attacks, so they never actually got to a PC. The riders were able to do cool things only because I bent the rules to allow their mounts to move and dash at the same time as the riders so they could ride up, attack, and move past, which is how they're intended to work. PCs were a bit peeved that enemies could move 120' as well as attack but they were the ones cast 6 Fireballs between the wizard and bard (using "Additional Magical Secrets")!
Fireball really destroys the battles. The next round is the two dwarf barbarians who move 30' with no range attack and only 95hp. Two free range attacks by the PCs before they can melee, assuming no one moves. At least the Dwarves can stay 45' apart so Fireball can't hit them both.
The finals has 3 Flesh Golems, who are especially vulnerable to fire! The Froghemoth conversion moves only 20', though it does get to move as a legendary action (good thinking). I'm pretty sure I'm just going to switch it for an Efreeti though. Immune to fire, super fast, and it can summon a fire elemental as assistance.
The battle wasn't a challenge at all - it felt like it was intended for lower level characters. It felt like Joren needed the raging ability - the conversion has him just as a druid but he needs the toughness. And I didn't know what a "janni" was (though I do happen to own Dragon #66 where they first appeared) so it threw me off when a PC asked what race he was. The conversion lists him as "elemental" which tricky. Maybe he should be a genasi?
There's also a discrepancy in the adventure. On page 36 the prize for the first round is 2,000gp, but on page 45 it says the price is 1,500 gp. And the Thieves' Guild offer from Tirra doesn't make any sense:
"For the final round, the bookmakers have offered the Thieves’ Guild special odds for wagers against Auric’s Warband. Tirra informs the PCs that if they can defeat Auric, Khellek, and their leatherworks (flesh golems), the Guild is willing to split a portion of their winnings amounting to 7,500 gp to the group if they’re willing to part with 2,500 gp of their own up front."
They meet Tirra at the dinner - are they supposed to put 2500gp up that they will win the whole thing? That seems a bit early to be throwing that kind of money away.
I did end up going with the conversion as written. I had planned on adding frost damage and some more +1 items to increase ACs, but as you said - there was a lot of moving parts so it was much easier to just check the sheet and go with it.
They really enjoyed the battle. They want more of a challenge next time, but they definitely got into it!
The barbarians will probably go down quickly, but have them quaff the potions of fly (60 foot fly speed), rage for damage resistance (all damage - bear totem, relentless rage) and fly with a double move. Keep them apart enough that the fireballs can only hit one at a time. Then have Loris (through a proxy) let them back in at night and try to kill the PCs in their sleep.
In the end, it isn't a bad thing for the PCs to do well in the arena matches. They have 3 days to stop the ulgurstata, and there is a lot of difficult stuff in their way in the ruins. They need enough left over in the tank to actually survive their nightly escapades.
If you swap out the froghemoth for an efreeti, make sure to have the misinformation be that the monster is going to be a froghemoth.
And yes, Tirra's proposal is a high risk/high reward offering the night of the welcome dinner. My group pooled their money together for that and managed to bluff their way to the bottom of the betting odds before betting on themselves through a proxy. The best part was the Strength 8 Tiefling wizard proudly declaring, "And I'm the tank!" and convincing all the oddsmakers around that he was serious. They were quite well off after the tournament.
I made the janni a djinni. Djinni are elementals in 5e.
If you use the flesh golems in the final battle , Khellek could have a few illusions (major image)of flesh golems on the battle field. Just make sure everyone is at least 40 feet from each other. I had Khellek maze the Oath of the Ancients paladin at the beginning of combat in my game (the group would huddle under him for protection from AoE spells).
I like your idea of illusions of more flesh golems. Force them to waste Fireballs! But Khellek doesn't have Major Illusion... Also, it's a 20' cube and just one Golem. And it's Concentration. Versus Maze, which just takes out a PC on the first round! (followed by Chain Lightning...)