The flavor of this card is pretty straight-forward: these are the ritualistic dagger the priests use for the human sacrifice to their gods. One is aligned to Horzatl and the other to Quiacatl. I'm trying to work a good set of abilities that do anything along the range of:
*) Make abilities cheaper on the creature that equips them
*) Add a sacrifice a creature: get an ability from the god
*) Punish someone from the other color that uses them
*) Power up the wielder versus creatures on the other side
I'm giving it a high casting cost but a low equip cost because I want this to be powerful, but once it's down I really want it to affect the game state.
Horzatl's Sacrificial Dagger

Artifact
Horzatl's Sacrificial Dagger can be attached only to a red or white creature.
Equipped creature has

, pay 2 life: Remove X poison counters and equipped creature gets +X/+0 until end of turn.
Equip

Quicatl's Sacrificial Dagger

Artifact
Quicatl's Sacrificial Dagger can be attached only to a green or black creature.
Equipped creature has

, sacrifice a creature: Creatures you control get +2/+2 and If this creature deals combat damage to an opponent, that opponent gets a posion counter until end of turn.
Equip
Current wording:
Horzatl's Ceremonial Dagger

Artifact
Horzatl's Ceremonial Dagger can be attached only to a red or white creature.
Equipped creature has
, pay 2 life: Remove a poison counter from yourself. Equipped creature gets +1/+1 until end of turn.
Equip 
Quicatl's Ceremonial Dagger

Artifact
Quicatl's Ceremonial Dagger can be attached only to a green or black creature.
Whenever equipped creature deals combat damage to an opponent, you may sacrifice a creature. If you do, that opponent gets 2 poison counters.
Equip 
Changes: 1) Fixed the wording slightly on Quicatl's ability. The point is until end of turn, your creatures power up and if they hit the other guy he gets a poison counter. The counters aren't supposed to be until end of turn - is there a better wording?
2) Changed the name to ceremonial daggers. Added art directions. Made Horzatl's dagger follow Eph's advice. Changed Quicatl's dagger to require a sacrifice on hit (so it will not take away 2 creatures). Thinking about adding some sort of drawback to Quicatl's if you don't sacrifice - more flavor but less useful and more cluttered.
3) Fixed the text so it actually has the same cardname as the card.