Use "Coffin Seller" along with "Gravekeeper's Servant", to make for a devastating continuous nightmare. Every time your opponent attacks then he not only looses a card from his deck, he also looses 300LP if that card happens to be a monster.
Use "Coffin Seller" in conjunction with "Vampire Lord"/"Vampire Lady" and declare a monster every time "Vampire Lord"/"Vampire Lady" does Battle Damage so no matter which monster is sent to the graveyard, your opponent loses 300 Life Points
This card can be used to put the hurt on a "Lightsworn" or "Dark World" user, as they will take 300 damage for each "Lightsworn" or "Dark World" monster they control (more or less) each turn.
Use this card in a "Venom" Deck, to inflict damage, each time a opponent's monster is destroyed by "Venom Swamp".
Use with "Dark Room of Nightmare" to inflict 600 points of damage each time your opponent sends a monster to his Graveyard, and inflict additional damage when destroying your opponent's monsters by battle or card effects.
Combo this card "Final Attack Orders", "Scrubbed Raid" and "Savage Colosseum". The opponent will be unable to attack as you would withdraw the opponent's Battle Phase, hence all their monsters would be destroyed by the Colosseum. Furthermore, the opponent would take 300 damage for each monster destroyed/unable to battle.
Use in a Beatdown deck to inflict further damage, forming a Beatdown/burn deck hybrid.