The SledgeHammer is the most powerful melee weapon in Dead Trigger 2. However, due to its weight, the attack rate is the slowest of all melee weapons currently present.
It resembles a big heavy duty hammer, which would do a lot of damage on its own, but its potential is further increased by iron spikes, added on it. However, as it's heavy the attack rate and movement speed are very slow. Later it may lose its one-hit kill ability and it has to be upgraded.