Well, since others have been doing it, I thought I might as well throw in some generic ideas that may or may not be made into cards. Again, feedback is always nice, but don't be a prick about it. This is for cards exclusively splashable into other decks, so lets see what we can come up with, shall we? I'll update this post whenever new ideas come to mind:
You cannot Xyz Summon while this card is face-up on your side of the Field. If you control an Xyz monster: Banish this card. When this card is Normal Summoned: you can Target 1 Non-Tuner monster in the Graveyard(s), whose level is less than or equal to this card's current level; Special Summon that Target. You may only control 1 "Archer of Bound Souls".
You cannot Xyz Summon while this card is face-up on your side of the Field. If you control an Xyz monster: Banish this card. Your Opponent cannot detach Xyz Materials from face-up Xyz monsters they control. Your Opponent cannot activate the effects of Xyz monsters, nor the effects of detached Xyz Materials. Face-up Xyz monsters cannot attack other Non-Xyz monsters. You may only control 1 "Seductress of Bound Souls".
2 Lvl. 4 monsters
This card is unaffected by the effects of Flip Effect monsters. If this card declares an attack: You can detach 1 Xyz Material, then Target 1 Set card your Opponent controls; Reveal that Target, then place it on the bottom of your Opponent's Deck. You may only activate this effect of "Sinister Seeker" Once per Turn.
When this card is activated: Banish 1 Equip Spell Card from your Graveyard and 1 separately named Equip Spell Card from your Deck that are both appropriate Targets for the Equipped monster; This card is treated as, and gains the effect(s) of, one of those Banished cards (your choice). You may only activate the effects of "Armed and Ready" Once per Turn.
You may only activate this card if you control no Xyz Monster(s). Target 1 Xyz Monster your Opponent controls; Banish all Xyz Material(s) from that card, and if you do, negate its effect(s). You may only activate 1 "Xyz Repent" per Turn.
Once per Turn, you can Special Summon 1 Zombie-Type "Guardians" Token (dark, zombie, atk: 0, def: 1000) in Defense Position on either Player's Field. These tokens cannot be Tributed for a Tribute Summoning, except for the Tribute Summon of a Zombie-Type monster. During your Standby Phase, if there are 3 or more "Doomed" Tokens on the Field: You can cestroy all Face-Up Zombie-Type monsters on the Field and destroy this card; Special Summon 1 Zombie-Type monster from your Deck, Hand, Graveyard, or Banished Zone. If this Card is Removed from the Field; Destroy all Face-Up "Guardians" Tokens.
Once per Turn, if you control only 1 Tribute Summoned monster (and no other monsters): Target 1 monster in the Graveyard(s) used for that monster's Tribute Summoning; Special Summon it to your side of the Field. You cannot Special Summon a monster with the same name by this effect more than Once while this card is Face-up on the Field.
Target 2 monsters with equal atk and/or def on the Field; take damage equal to the highest combined atk & def of one of those monsters, and if you do, Banish both monsters.