ok, all Admins and Mods are able to use these two cards, but they won't help much unless you run a fiend deck.
the first:
The Description says:
This card cannot be Normal Summoned or Set. This card can only be special summoned from your hand to the field by removing from play 3 level 6 or higher Fiend monsters in your Graveyard or Special Summon from your Graveyard. As long as this Card remains face up on the Field, halve the ATK of all your opponents Monsters. During the damage step between this card and a Defence Position monster, inflict the difference between the ATK of this Card and the DEF of the monster as battle Damage to your opponent.
And the Second:
Effect:
This card cannot be Normal Summoned or Set. This card can only be special summoned by Tributing one "Hellfire Demon" on your side of the Field. When this card is summoned, destroy all other cards on the Field. This Card cannot attack on the Turn it is summoned. Negate all of your opponents Monster Effects as long as this Card is face up on the field.