Struggling with this level alot!! there are so many of them!!

Mana crystal
Wall blades
Floor spikes
Barricade
Sticky tar
Bomb
Catapult
Skeleton

Put a barricade at the first tile of the lower or upper corridor. Heroes will not try to bust through it and instead look for another way around, heading down the other corridor. Pack it with wall blades and floor spikes. At the end of the corridor a barricade and catapult. Sticky tar, bomb, and skele to pack on the dmg.

Here's how I do it.

1. Lots of mana crystals, on the far right, so that you have lots of points to spend.
2. Try to keep the heroes in the front vertical corridor.
3. Replace the living walls as fast as you can, but place them in the doorways, not in the corridor. A lot of the heroes will walk past the walls looking for an opening, giving you more time to damage them.
4. Shooters behind the living walls. Lightning towers, triballistas - whatever you have. Put more shooters in that vertical column, so that any hero that gets past your living wall gets zapped by multiple shooters.
5. If you lose a living wall and can't replace it yet, drop something disposable in the spot, such as a mana crystal (to stall the heroes a short time) or a bomb.
6. Wall blades or wall press in that vertical corridor where the heroes are trapped.
7. Optional: floor spikes or perforator in the spot behind the living wall, instead of a shooter there.
8. Whatever disposables you like to use for taking out heroes in that vertical corridor. Bomb, rock drop, slime, etc. You need to hit the epics at least once or they are likely to get through both the living wall and the shooters behind it.