Strategy
Mouse
It is impossible to beat this map without the help of the shaman. Wait for the shaman to build. Be sure not to dive (↓/S) too much. If you go off-screen, you die!
Shaman
Create a build of nails, anvils, and long planks.
Alternatively you can place 2-3 springs, although mice who miscalculate will die, so creating a construction out of planks will be much more secure and will give you a lot more saves.
You can also use a cloud if you got the skill, and perhaps a bridge totem if you have one in Hard mode.