This is pretty straight forward but the description might mislead some people.
Go to Single Player > Free Play, then with Slate selected in the level list, hit
to select modifiers, and set the following modifiers:
In mode, change the Type from Survival to Area, set Size to Small and Duration to Short. Leave the Player all modifiers disabled, then switch the Arena type to ice.
A lot of this achievement boils down to luck and where the areas spawn, but once you've exceeded 75%, the achievement will pop as soon as you die.
Note: several commenters are saying theirs only popped once they exceeded 100%. That was not a requirement for me, so YMMV.
Try to get the most you can out of the first few areas while the level isn't too busy yet, then as things heat up, just go for areas as you easily can, but maintain the bigger priority on staying alive. Once I stopped worrying about getting the most out of each area I was hitting 60% pretty consistently, and finally hit 80 on the unlocking attempt.