Pretty tough to die here, as enemies don't move. So if you are having issues, simply start the level and go shower or make food.
Unlocking the level is harder than the achievement, you'll need to beat any previous level (which is to say, survive 30 minutes). This will unlock Molise.
Mad Forest is probably the easiest to beat. Playstyle is up to you, but I used Poe (unlocked by getting Garlic to level 7) and maxed out the Garlic. Garlic will push most enemies back or outright kill them, combine with the Heart (red, not black) to evolve it, or use with Bible for extra knock back.