Lava cracks upgrade two, and I repeat, two defenses I don't have. Let's change that, shall we?
Flambé-ista: Ballistas have been combined with lava to burn heroes, dealing twice the damage.
Lava bridge: Combine with tentacle gardens to create health stealing floors.
Mana crab restore: Restore the mana crab's health by placing it onto lava cracks or bridges to repair.
Lava wall: combine a barricade with a crack to create a longer lasting wall, and damage heroes in the process.
Twin blaze: Start a fire blast on a lava crack to make it stronger.