To get this, beat the 4 Ice world levels (which is world 3) and it will unlock when you enter the first Temple world level.
Since every level is randomized, there is no easy walkthrough possible for the Ice world levels. Some tips:
- the lower third of the level is just an abyss. Don't drop down before looking (hold down to scroll the screen down). On the plus side, the Ice world levels aren't as big as those in the two worlds before it.
- the ice is slippery. If you stop running, you'll slide for a bit before coming to a standstill.
- Yetis are harmless but very strong. They will throw you around, often into a hazard, losing you hearts. If the level feeling mentions 'it smells like wet fur', King Yeti is in the level - he's more dangerous but will drop a special item if he is killed.
- Watch out for mines (small red lights), if you touch them they will explode after about 1 second.
- The flying UFOs shoot a (slow-moving) laser straight down if you pass below them.