most difficult map to play true solo
River Reik. notorious boat event. reaching there is already lengthy then you need to defend yourself in narrow space with constant horde attack while breaking chains, lastly putting barrels. You doing all these tasks on your own simultaneously. Nearly impossible on nm/cata.

most difficult level on onslaught cata
Trial of Foolhardy. before entering first room take a deep breath because you won't gonna breathe again

I had an idea of similar post months ago, many aspects to consider...

I think difficulty of a map can be judged by these factors:

(1) difficulty spikes
(2) item availability & locations
(3) level of coordination required
(4) respawn locations
(5) reliable strategy for events
(6) required number of players for events (DPS check etc.)

Vanilla map, full team full book run:
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Rank A:
- Reaching Out (with/without exploit) (level of coordination high, no reliable strategy, require many players to pass)
- Summoner's Peak (level of coordination high, no reliable strategy, require many players to pass)
- River Reik (level of coordination high, no respawn point in finale, no extra item other than what the team carries, require many players to pass)
- Dungeons (easy to mess up in the dark portion, no respawn point in finale, level of coordination medium, difficulty spike: no room for the first ogre fight)
- Cursed Rune (level of coordination high (depending on holding position), no respawn point in finale, no extra item other than what the team carries)
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Rank B:
- Trial of the Foolhardy (without exploit) (requires coordination if someone died and the team needs to start from the bottom, difficulty spike in the iceberg room, lower than average item count but no books)
- Well Watch (both wells, without red trueflight) (level of coordination high, require many players to pass, DPS check)
- White Rat (without bombing ogre) (respawn points are hard to reach with ogre alive)
- Waylaid (no item in inn, respawn points are far in finale)
- Castle Drachenfels (no respawn point in finale, respawn points are far in escape section)
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Rank C:
- Horn of Magnus (no respawn point in finale and in middle event, but team can have 4 healing items in finale, difficulty spike: RNG in finale)
- White Rat (successfully bombing ogre)
- Chain of Fire (without exploit) (no respawn point in finale)
- Reikwald Forest (no respawn point in middle event)
- Trial of the Foolhardy (with exploit)
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Rank D:
- Supply and Demand (no item in finale)
- Wizard's Tower (items in finale depends on RNG, DPS check)
- Khazid Kro (no respawn point in middle event, no item in finale)
- Engines of War (no respawn point in middle event)
- Well Watch (with red trueflight)
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Rank E:
- Garden of Morr (no respawn point in finale, but requires few players to pass)
- Enemy Below (no respawn point in finale)
- Courier (no event spawn at all)
- Smuggler's Run
- Black Powder (plenty of items, possible to speed run)
- Wheat and Chaff (ok amount of items, possible to speed run)
- Chain of Fire (with exploit)
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Rank F:
- Man the Ramparts (plenty of items, low difficulty, possible to speed run)
- Waterfront (plenty of items, low difficulty, possible to speed run)
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Rank ?:
- Town Meeting (depending on waves)
- The Fall (depending on waves)
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I haven't attempted onslaught cata on all maps, but some maps do feel ridiculous:
- Summoner's Peak (3rd generator spawns infinite ogres + patrols + specials + hordes)
- Trial of the Foolhardy (infinite patrols + hordes + specials, multiple ogres)
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Harder ones are probably:
- Reaching Out (specials in Krench fight, bombs can't stagger Krench according to code)
- River Reik (specials in boat fight)
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Probably require Drakefire Pistols to pass:
- Castle Drachenfels (infinite patrols + hordes, but lesser special threat)
- Man the Ramparts (infinite patrols + hordes)
- Horn of Magnus (24 extra SVs + SVs from hordes in finale, but strength bombs will do)
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Multiple Ogres:
- Black Powder (2)
- Trial of the Foolhardy (2+1 in iceberg room)
- Wheat and Chaff (3)
- Waterfront (4 in finale)
- Well Watch (3?)
- White Rat (2 on top floor)
- Castle Drachenfels (2 in finale)
- Dungeons (2 in finale)
- Summoner's Peak (1 if you can defend the 3rd generator, 1+1+1+... if you can't)
- Khazid Kro (2 in middle room)
- Cursed Rune (1+1 in finale)
- Chain of Fire (2 in finale)
- Reikwald Forest (2+1 in finale)
- River Reik (possible double ogre in the swamp? 1 regular and 1 extra)
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I don't do much True Solo myself, so here is my impression from watching true solo videos:
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Never attempted:
- Wizard's Tower
- Reaching Out
- River Reik
- Waylaid
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Exploit:
- Summoner's Peak (wait for clan rat wave)
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Old patch:
- Well Watch (Old Bolt Staff)
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Notable:
- Horn of Magnus (runner in finale will be a pain)
- Man the Ramparts (not that easy from personal experience, no cover for specials and tons of stormvermins mixed with trash rats; though there are tons of exploits too)
- Enemy Below (no experience but the escape seems hard)
- White Rat (seems hard according to videos)
- Castle Drachenfels (escape section is hard)
- Dungeons (can't hold torch and fight at the same time; most parts aren't true solo friendly)
- Khazid Kro (steam room is time race)
- Cursed Rune (finale is hard, seems to require kite loop, no cover for specials and not many ways to fight SVs + horde)
- Trial of the Foolhardy (iceberg room and survive section are hard)
-------------------------------------------------

The differences of bots and human team (aside from bots being weaker than capable cata human players):
(1) Bots don't do human objectives (break chains, carry stuff, carry torches, consciously defend wells, etc.).
(2) Bots don't follow tactics (rush, watch over a fixed direction, etc.).
(3) Bots can't kite.
(4) Bots can get stuck.
(5) Bots have low ogre DPS.

Because of (1) and (2), all maps that require high level of coordination are harder with bots.
There aren't many situations in based game maps that require the team to kite, probably the only one is the iceberg room in Trial of the Foolhardy when 2 ogres show up, or some minor kite in the skull room in the Dungeons, so (3) doesn't have much effect. (4) can be mostly avoided by map knowledge and team pathing. (5) seems true although in QOL / VMF bots prioritize ogre over all other rats, so I think the issue is that they die from other rats before doing enough damage to the ogre. This makes maps that require killing ogre fast harder.

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Harder ones with QOL / VMF bots:
- River Reik (even on nightmare)
- Summoner's Peak
- Reaching Out (bots don't know how to fight Krench and bots have low Krench DPS)
- Dungeons (it's harder for player to kill specials and SVs in the dark portion while carrying the torch around, ogre DPS needed in finale)
- Well Watch (unless the player has red trueflight and kills everything on their own...)
- Trial of the Foolhardy (likely all bots die very quickly in the iceberg room while humans can last longer)
- Black Powder (if you use a lot of shortcut jumps that bots can't follow, and humans have to carry all barrels so the time taken to complete is longer than with humans)
-------------------------------------------------

yeah in black powder the bots tend to not be able to follow the human player whos zigging and zagging all over the map to avoid choke points and to get the barrels there fast. the bots tend to fall behind somewhat, at least for me they do.

I don't really understand why you keep mentioning the red trueflight, it's traits are pretty terrible.

Reaching Out and River Reik are fairly easy maps to play with bots, provided that you know how the handle the events and prepare accordingly. Obviously going in as Saltzpyre on a greatsword is setting up for failure, but there isn't much to them otherwise.

You can still solo Well Watch with a hagbane, if you abuse a certain cheese spot.

https://www.youtube.com/watch?v=oUl2lGau-GE

Red Trueflight kills >80% of the horde with 175% horde size. (EDIT: Nevermind, I was using attack buff, I will find another video when I have time...)

EDIT:
https://www.youtube.com/watch?v=ydQsFDFsXZ4

Scoreboard figures do not fully represents the well defense section because I am not trying to kill all the rats with trueflight when I was not defending... but you can trueflight either kills the whole horde, or reduce the number to a point that there is no pressure to finish the rats by melee.

I really don't see how you can play Reaching Out full book cata with QOL bots and not having them die 2-3 times and you only have one guaranteed heal. Maybe you should make a video for that.

I don't think the damage buff is actually that impactful on TF's performance. It helps with left clicking clan rats away, but the horde melts all the same. Unless the arrows also pierce extra targets due to the buff?

Anyway, returning to bots on RO. Even if they die it mostly doesn't matter. The only challenging bit is the end. Having the bots survive is mostly a case of luck and of managing to glitch Krench's summons. The only book that you cannot lose is the grim if you make that a goal for yourself. I wouldn't as I find it too luck dependent. :D

Maybe I'll try it at some point, but without books and no practice it was pretty breezy.

Just completed Stormvermin Mutation mod on all nightmare maps except Trial of the Foolhardy (my mod with fewer and weakened ogres), here is my list of harder ones, mainly these are maps that require you to hold a position for several minutes (MistLight can supply additional information):
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- Horn of Magnus (inn, rooftop, finale)
- Smuggler's Run (gate rooms)
- Wizard's Tower (finale)
- Man the Ramparts (cliffs)
- Waterfront (warehouses; might be a good idea to have some players stay outside)
- Well Watch (large SV hordes)
- White Rat (large SV hordes and cliffs)
- Dungeons (finale)
- Khazid Kro (steam room and corridors)
- Chain of Fire (middle event and finale, more difficult if played honestly)
- Trial of the Foolhardy (large SV hordes and many multiple-ogre fights)
- Waylaid (inn !! ... and finale)
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Well, I listed 12 maps out of 25 maps...

Other maps with no guaranteed ammo crate might be difficult in those situations, but on nightmare it's still ok to kill (weakened) ogres by melee.

These are other 13 maps that worth to mention their hard parts:
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- Wheat and Chaff (easiest SV mutation map, few SV hordes, plenty supplies)
- Enemy Below (high ogre spawn rate, bell spawns 4 ogres if you use, some cliffs, tunnels)
- Black Powder (cliffs, large SV hordes with ogres)
- Garden of Morr (crypt, gardens, finale)
- Engines of War (doomwheels, finale)
- Supply and Demand (finale)
- The Courier (tower, tomb)
- Reaching Out (back alleys, boss fight)
- Castle Drachenfels (corridors, finale)
- Summoner's Peak (bots not recommended, cliffs, large SV hordes)
- Cursed Rune (ravines, finale; large SV hordes with ogres, ammunition might be problem)
- Reikwald Forest (unavoidable patrols, drop down middle event, finale; only 1 ogre with large SV hordes)
- River Reik (unavoidable patrols, finale; possible large SV hordes in boat fight if SVs not pushed/killed and chains not broken quickly, minimum 3 ogres fight after boat event so save some ammunition)
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I'd played most of the maps with 200 ping, dodging and kiting ogre is doable. SVs might give trouble with that ping though.

I don't think Enemy Below has higher ogre spawn rate (it is special spawn rate afterall), but the notable mention is the single-plank bridge section where you have a tedious wait of the death of all ogres and SVs in order to cross safely.

BTW I think players receive no fall damage when they are punched flying by ogres. (If there is a list of less well-known mechanics somewhere...)