Valhalla Gate

Valhalla Gate, more specifically Valhalla Gate Another, is one of the most powerful beings in the series as it can kill absolutely anyone it is cast upon, for a great price however

Appearance
It consists of 2 parts, the first being the actual gate itself, and the other is the sentient statue placed on top of it.

The gate itself appears to be styled after a 'hellish gate' of the sort, having spikes all over it, and an over devilish look.

Atop the gate is a sentient, male, stone statue. It is primarily grey with white eyes, lacking pupils. The statue is always seen smiling. Off notice, while the gate can only open and close, the statue can freely move its arms

Personality
While the gate itself lacks personality the statue does have a personality. It's most notable trait is that it's constantly laughing. It is also very aware of how strong it is, reassuring Mash that the Demon Lord is in the void, and will not return. It also takes joy in the fact that whoever cast it will die, laughing at Seiya for it. Despite this, it claims to be fair, as it always takes the 'toll' at the same cost (namely, the casters life) It calls itself a servant of the underworld.

Powers and Abilities
Since it can kill anyone, regardless of how strong they are, it is one of the most powerful beings in the series. Whereas the Demon Lord was capable of escaping the original Valhalla Gate it was not capable of escaping Valhalla Gate Another (namely due to the fact that Valhalla Gate Another swallowed the orginal Valhalla Gate as well). However when summoned it will also kill the caster. Valhalla Gate Another also mentions that while you can escape the death of the original Valhalla Gate, no one can escape the death of Another. It is not known if Valhalla Gate Another actually kills his enemies or not as he mentions that 'the Demon Lord is in the Void and will never escape', thus making it a bit vague whether he actually kills or not.