Iron Man Guide
This world is just a matter of learning how the levels/hazards work and how to get past them easily.
My Recommended Order
6, 17, 18, 19, 20, 10, 12, 1, 2, 3, 4, 5, 16, 15, 14, 13, 12, 11, 9, 8, 7
(Use The Kid unless I say otherwise)
All level ratings are relative to this world's levels only.
Run all the way. All the obstacles aren't too tough and the area is large enough that mistimed jumps aren't a problem.
Stick to the wider walls instead of the narrower ones and you'll have no problems getting through this.
Simple obstacle course. Just go right, grab the key, and backtrack to the start.
3-4 (Use Meat Boy)
The Kid has issues with jumping to the conveyor belts here, so just use someone without a double jump. If you stay in the air a lot, this stage isn't a problem.
A vertical level with no hazards other than a bottomless pit. Definitely shouldn't pose a problem at all.
Ride the first 3 conveyor belts up. When you get on the 4th one, you need to jump off it yourself when you're at the top of the belt. This can be tricky to pull off at first, so I suggest doing this level as one of your first 5.
Start at the bottom of each conveyor belt when you get on them, and you should be able to get through each pit easily.
This level introduces the missile launcher, the world's main obstacle. It basically fires a homing missile at you at regular intervals. Every launcher has a different cooldown rate before it fires again, so it's worth noting that you might be retrying levels that have these hazards often until you get their timing down. As a general rule, being on the run and constantly moving is a good way to dodge them.
For the level itself, just keep moving and try to bait missiles to land on walls before you finish climbing them.
Ride the conveyor belt, jump to the left wall, then jump right to break the blocks, and jump left again so the missile doesn't get you. Grab the key and just fall to the left and keep moving right when you're under the launcher.
Drop down, and wait for the missile to launch, then run over the breakable blocks and back off a little. After the launcher fires and misses you, drop down. Repeat.
Just can either run through the whole level. There's only one obstacle you need to jump over.
You can jump through a small gap between the first two gears at the bottom, and just climb all the way to the top at your leisure. It's a bit risky, but not if you make this one of your earlier levels. If you want to do this the normal way, just hold run and start climbing the left wall, then jump right when you reach the big salt wall. Jump left again once you're above the salt wall, and just continue climbing.
Don't hold jump. Just take it slow and easy and you'll clear this in no time.
Just a regular platforming stage. Nothing noteworthy here.
With double jump at your command, this stage is easy. Just keep climbing the right side.
Just keep holding the run button and save your extra jump in case you mistime your first jump, and this is an easy level.
Jump from wall to wall to get to the key, drop to the bottom to get the other key, and go to the top again. I suggest doing this for your first level because the chance of getting nailed by a missile is high.
Jump over the gears as they pass, and at the 8 second mark, the key should be low enough that you can grab it easily. Just head to the start and wait for the locks to break, while dodging the occasional gear.
Make a hole you can jump through with the floor you start on. After dropping to the middle level, move under the blocks so the launcher on top won't fire anymore. From there, you just need to jump over the occasional missile from the 2nd launcher, and you're home free.
When you reach the chamber with the first launcher, wait at the entrance so it sees you and fires. Move out of the way and climb the wall. Wait for it to fire again before climbing to the top. Once you grab the key, stay on the platform right of the missile launcher and just keep jumping until the locks break.