Here you can find few tips that might help you to beat mall level on hard.
Mall Level Tips
You want the turrets in front of the cave portal built for sure.
- I was using laser turrets until I attacked it, then I switched to the volley ones, they seem to stun the big dudes and do splash damage.
Backpedal away from every large enemy, never let your dumpster take those hits unless you have to (big crabs can catch up).
Push your way up with the dumpster until a big one spawns.
- Then keep it in range of your archers, but backpedal enough to not get hit.
- Dropping coins as you pull the dumpster back gets rid of those pesky masked greedlings.
I had enough archers that even if the big crabs overran me I could just go back and buy another dumpster/robot combo, then push up again.
The last 3 or 4 wall segments – I never built.
- Building all of the turret towers and barricading them, protected my front line and let me backpedal away from everything.
The only waves that reached me were blood moons.
In cave advice
The mechanic will repair the dumpster in the cave! But if you see a greed unit on the screen, she probably wont.
- Standing idle on the other side of the dumpster from her seems to help her decide to do it in cases where enemies are not present.
Backpedal all the way to the cave entrance to avoid taking big enemy hits or just to repair if necessary.
I killed a spawner, retreated to the cave-mouth, fixed dumpster, repeat.
Just remember to keep those big guys in range of your archers or you backpedaling to the entrance may just end up trapping you.
Also your companions bike charges knock crabs over and stop their crab-charges.