Pretty much ALL of the last 10 levels of Mayhem are misplaced:
21: It's not that hard at all if you realise that large gap in the middle can be dug through. In fact, the hardest part for me was getting the basher at the end to go the right way
22: Neat looking level, but come on, I made a custom of this with 7 fewer of all skills. Either cut back the skills or move this down to much eariler in Mayhem.
23: A bit harder, but really still not that bad. Should be an earlier Mayhem, not last 10.
24: Should not exist, but this isn't even Taxing.
25: No harder than the tricky equivalent.
26: This was really easy for me. May be harder on other versions, with only 10 of all skills).
27: There's a lot easier levels in this list, but this still seems easy for last 10.
28: Same as 27. This could so in mid-Mayhem maybe.
29: Well... yea, can't complain about this one.
30: It's FAR too easy, but this is meant to be a sort of "epic" level so it's OK.
I always thought some of the earliest levels in the last two sets are the hardest, so:
Mayhem 1: A great starting level for the set, but I think this is one of the hardest levels in the game for some reason.
Mayhem 5: Should be a last 5 level, this is really freaking hard.
Mayhem 9: This also gave me problems as a kid.
Taxing is FAR worse, though.
Taxing 1: Way too hard for the "intro" level of the set.
Taxing 2: Way too freaking easy considering the last level.
Taxing 3: Way too hard for level 3.
Taxing 4: Still quite hard for early Taxing.
Taxing 11: Could conceivably be in the last 10 mayhem levels, wow this is hard to pull off.
Taxing 12: Really? This should be like first ten Tricky.
Taxing 17: Remove the left exits, then this level is fine. As it is, it's literally no harder than the Fun version.
Taxing 24: I like this level but come on this is really easy.
Taxing 26: Can be (early) last 10 Mayhem.
Taxing 29: yea I don't know either
So I guess my last ten levels in the game would be, if I had to order them:
Mayhem 21: The Far Side (this is harder than all the levels after it until No Added Colours)
Mayhem 22: The Ascending Pillar Scenario
Mayhem 23: BeastII, with 4 of all skills, 10 builders instead of current skillset.
Mayhem 24: Mind the Step
Mayhem 25: Triple Trouble
Mayhem 26: Just a Minute (Part II)
Mayhem 27: Down, Along, Up (yes, this is 3rd hardest level in the game. No, really, it is)
Mayhem 28: No Added Colours or Lemmings
Mayhem 29: Save Me
Mayhem 30: Rendezvous at the Mountain
.
And I'll get started on ONML later, because it's a LOT worse than Lemmings was