Fun
5 - So Close ... And Yet - Added steel
9 - Have a Bash at This - Minor changes to remove Blocker
10 - Well That's One Group Solved... - New level
13 (was 12) - Two's Company, Thirty's A Crowd - Minor terrain tweak
14 (was 13) - Just Dropping In - Terrain tweak

Also Fun
4 - Most Valuable Lemming - Terrain tweak
8 - Tree Top Trouble - Replaced with Rescue Rodents from Not Fun rank (Rescue Rodents unchanged, Tree Top Trouble deleted)
9 - Impact Zone - Replaced with new level, Crystal Cavern
11 - Temperature Drops - New level
12 (was 11) - Iron Awe - Terrain tweaks + major skill changes + lower save requirement
13 (was 12) - The Dire Docks - Major terrain changes

Hard But Still Fun
2 - Once You Pop You Can't Stop - Terrain tweaks + many less bombers + higher save requirement
5 - Recession Proof - Filled in terrain holes just in case you get unlucky with basher, no change to solution
8 - Pillars of the Community - Added steel
9 - Slow Motion - Redone top trapdoor area entirely
10 - Master Exploder - Remove a Bomber
14 - The Bridge Is Out - New level
15 (was 14) - The Ultimate Quest, Take 3 - Terrain change. This shouldn't impact the solutions of the other Ultimate Quest levels, although the same change has been made to them too.

Not Fun
3 - Mined Your Head - Replaced with new level, The Great Firewall
4 - Rising Condensation - Terrain tweak
5 - Rescue Rodents - Moved to 8 Also Fun position and replaced with new level, Crag David
7 - Down the Tubes - Major reworking
9 - The Firing Squad - Terrain changes
10 - Pain Factory - New level (I suspect if any of the new levels are riddled with backroutes, it'll be this one)
11 (was 10) - Offshore Rig - Minor terrain change
12 (was 11) - Toil - Major reworking
13 (was 12) - The High Ground - More steel and minor terrain tweaks

You have to send everyone the long way round. Just construct a path and you should be fine.

Spoiler

The most difficult part imo is how to get everybody past the machine gun robot trap. If you're getting mad at execution, then it may help to know that is expected that every lemming use every teleporter.

A simple spot-the-trick level. With so few skills you don't exactly have many options. It should be clear what two skills are required for the crowd to walk to the exit so that will reduce your options further. If you're still stuck, re-read my generic skill hints above.

The place you use the platformer should be the most obvious skill use. The rest of the level is a turn-the-lemming-around puzzle.

Spoiler

Multiple turn-the-lemming-around puzzles actually. And how are you going to cancel the attractor? Might need some double-duty skill use.

Spoiler

If you can't turn around your jetpacker after using it, what if you turned the lemming around before using it?

Hopefully it is clear your goal is to get someone to teleporter 3, and you can only do that by magnobooting from teleporter 1. Well, you'd like to, but something else needs doing first.

Spoiler

You'll need somewhere to stand to do that though. Sadly there is no elevator. Well, maybe you can use a series of steps.

There are a range of solutions here. Hopefully it is clear how you dig through the ground, you just need to find a safe way to do it.

Spoiler

I send a magnobooter the long way round each side, to construct a safe ceiling on the opposite side.

Spoiler

If you're struggling to get the last blasts done, you can send one group to the bottom and dig out the other side from underneath.

The attractor isn't only useful for crowd control. It also indefinitely stalls a lemming until you use another skill on it.

Spoiler

If you can't create a hole to detach a magnobooter in, try doubling up on bazooka shots.

Spoiler

If you're struggling to find a good place to use the laser blaster, maybe you're using the wrong lemming.

The most direct path for the crowd is the best one, but there are some issues constructing platforms in the correct direction. Yes it's another turn-the-lemming-around puzzle!

Spoiler

The first suitable place to turn around a lemming is closer than you think.

Spoiler

There is no suitable turnaround place in the second half of the level. Maybe you need to make one.

OK, there's a lot going on here. First concern is the main trapdoor, the lemmings will make their way over to teleporter 1 quickly. You need time to construct a platform to the exit, but there's no crowd control. And a platform isn't even long enough! Is this correct? How are we rescuing the upper-right trapped group if we don't do this? Do we really have to use the laser blaster to free them?

Spoiler

Well, we have 20 Jumpers which can cover the extra distance the platform can't, but we still need to delay some lemmings, and we can't spare any jumpers. Or wait, can we? Are we actually sending 20 lemmings to teleporter 1?

Spoiler

Sure would be nice to get someone over to teleporter 3. And it would be great if they could take their sweet time. Shame about the machine gun robot. How can you avoid this?

Spoiler

You don't need to save a magnobooter for the other side of teleporter 3 if you are already using one, so if you need to delay even more lemmings at the start, and also don't have enough jumpers, then why not give the other lemming some company?

At first this is another turn-the-lemming-around puzzle, but with magnobooters. And it is, but there's a little more going on here. Remember: if you can't find a place to turn a lemming around, you can always make one.

Spoiler

Should be clear we are eventually going to need to platform our way over to the teleporter, either directly or in a way we can magnoboot into it. But this offers us up another problem, if we cover up all the gaps to get to the exit, how do we laser blast a way into the exit at the end?

Spoiler

Not every gap needs to be completely covered up. But you are thinking too close to the exit. Think further out.

This level looks familiar. Why would I repeat a level? Let's be real here, I wouldn't make you do this twice unless it was a very different solution to the first time. I mean very different.

Spoiler

If you were wondering if the first level had a really devious and sneaky backroute, with the trapdoor being so close to the exit, you're right! Well, it wasn't possible before, but you can do it this time.

Spoiler

There's nowhere to turn a lemming around near the entrance. So we'll just have to find somewhere further away. Much much further away. What's the quickest way to get there?

Spoiler

If you were hoping you could skip the majority of the level, well, someone's going to have to traverse it all eventually. You should have the tools to take a totally different path this time.