An idea, that I want to expand upon

[Toffee.]

Deadly Combatant - Dino Claw
FIRE / Level 4
[Dinosaur/Effect]
Cannot be Set. If this card is Summoned, you can Send 1 "Deadly" monster from your Hand to the Graveyard: Draw 1 card. If this card battles an Opponent's monster, you can Discard 1 (only) "Deadly" monster: This card gains ATK equal to the original ATK of the sent monster, until the end of that Damage Step. The effects of this card are only applied if you have no Spell/Trap cards on your side of the field and/or in your Graveyard.
ATK / 1000 DEF / 800

Deadly Arms - War Shell
EARTH / Level 4
[Machine/Effect]
If this card is Sent to the Graveyard, you can target 1 "Deadly" monster you control: target gains 500 ATK. Once per turn, you can switch the original ATK and DEF of this card, until the End Phase. If this card destroys an Opponent's monster as a result of battle: Add to your hand 1 "Deadly" monster from your Deck, except "Deadly Arms - War Shell". The effects of this card are only applied if you have no Spell/Trap cards on your side of the field and/or in your Graveyard.
ATK / 1000 DEF / 2000

Deadly Law - Saber Hero
LIGHT / Level 4
[Warrior/Effect]
You can Tribute this card to activate 1 of these:
•Banish 1 other "Deadly" monster in your Graveyard: Special Summon 1 "Deadly" monster from your Deck.
•Target up to 2 Spell/Trap cards on the field: Destroy the Target(s).
You can only activate 1 effect of "Deadly Law - Saber Hero" per turn. The effects of this card are only applied if you have no Spell/Trap cards on your side of the field and/or in your Graveyard.
ATK / 1400 DEF / 1400

Deadly Virus - Technomancer
WATER / Level 4
[Fairy/Effect]
You can Pay 1000 Life Points: Special Summon this card(from your Hand). As long as this card remains face-up on the field, Increase the ATK of all "Deadly" monsters you control by 300. If this card is selected as an attack target, you can Pay 1000 Life Points: Change the attack to another appropriate monster on your side of the field. The effects of this card are only applied if you have no Spell/Trap cards on your side of the field and/or in your Graveyard.
ATK / 0 DEF / 1200

Been buzzing around in my head for a few days.
Not sure what to make of it.