Let's make a ridiculously overpowered mess!

[Medivh]

Ultimate Chaos King Dragon Knight - Harbinger of Creation and Destruction -
Dragon / Effect
LIGHT
Lv. 10
ATK: 4000
DEF: 3600
This card cannot be Normal Summoned or Set. This card can only be Special Summon by banishing 2 LIGHT and 2 DARK monsters from your graveyard. This card's Attribute is also treated as DARK. This cards' summoning cannot be chained to. Once per turn, you can banish any number of cards in your hand to banish 1 card from either side of the field for each card you banished. This card cannot attack the turn you activate this effect. During the End Phase: Your opponent takes 800 damage for every banished LIGHT and DARK monster.

I know this is broken. It's a Chaos monster - it's [i]supposed [/i]to be.

[Anbu-of-Sand]

The card doesn't seem that overpowered. To get out both Chaos Monsters you'll first need to banish out a total of 2 LIGHT's and 2 DARK's from your Graveyard (which isn't too hard nowadays). From there the card is going to be annoying / really scary. The effect however could be worked on. I can see what you're getting at with the dual Type and Attribute, but it feels unneeded (the Type that is). The effect itself when it comes to discarding and banishing doesn't seem overpowered (even though discarding could be a plus). The 200 burn really seems random and unneeded as well (at most you're only going to deal what, 1000?), it should be higher if it were to resemble a combination of both, perhaps 500.

If you want to really make this card broken, make it so once per turn you can banish one card on the field for every BLS and every CED in your banished pile. This makes it so you're opponent will NEED to get that card out of the banish zone if they don't want to keep on getting screwed over, and you don't have to keep on destroying your hand in order to get a few banishes off for a single turn, and might as well give it the effect where if it banishes it can't attack that turn (unless you intend on keeping it as a finishing card). And with it's Summoning Conditions being so 'situational', perhaps adding to the effect where it's Summoning cannot be chained too could be nice as well. This way you're opponent can't say Torrential Tribute or Solemn Judgment itself, but will be able to say, Torrential Tribute or Bottomless Trap Hole if you choose to summon another monster afterwards. Perhaps make this the effect to make it more 'broken' / reasonable:

[i]This card cannot be Normal Summoned or Set. This card can only be Special Summoned by banishing 1 "Black Luster Soldier - Envoy of the Beginning" and 1 "Chaos Emperor Dragon - Envoy of the End" on your side of the field. The Summoning of this card cannot be negated. This card's Attribute it also treated as DARK. Once per turn, you can banish any number of cards in your hand to banish the same number of cards on the field. This card cannot attack the turn you activate this effect. One time only, you can banish all cards in your hand and inflict 500 damage to your opponent's Life Points for every banished LIGHT or DARK monster of yours.[/i]

You might as well make the stats 4000/4000 too, since it's intended to be a boss (monster).A more balanced version:

[i]This card cannot be Normal Summoned or Set. This card can only be Special Summoned by banishing 2 LIGHT and 2 DARK monsters from your Graveyard. The Summoning of this card cannot be negated. This card's Attribute it also treated as DARK. Once per turn, you can banish any number of cards in your hand to banish the same number of cards on the field, and take 200 damage for every card banished from the field. You cannot conduct your Battle Phase the turn you activate this effect. One time only, you can Tribute this card to and banish all cards in your hand to inflict 400 points of damage to your opponent's Life Points for every banished LIGHT and DARK monster of yours.[/i]

From here you can make it 3500/3500 to make it somewhat balanced. I don't know really, since it's somewhat unplayable in my opinion. Just thought it'd be fun to play around with this card and somewhat make it one of the best / most funnest Chaos monsters out there. But yeah, hope this helped.

[Medivh]

Ok, thanks.