Mot and beiji for now

|Mot, Canaanite God of Death|???|????|Fiend/Effect|Earth|8||2500|2800|Cannot be Normal Summoned. When this card is flipped face-up on your opponent's turn: Target 1 face-up monster your opponent controls; Change this card to face-up Attack Position and destroy that target. Once per turn, during your Main Phase: You can flip this card face-down.|

|Beiji Weng, the Lord of the Northen Hemisphere|???|????|Fiend/Effect|Water|7||2100|2900|When your opponent activate a card or effect that would target a monster(s) you control to leave the field while this card is face-up in Defense Position: Your opponent can discard 1 Spell/Trap Card to negate this effect otherwise, target a monster your opponent controls in subsitution of your monster(s) targeted by the card or effect your opponent controls instead. If your opponent controls no monster for this effect: Negate the activation and if you do, destroy it instead.|

First of all I think flip-effect tribute monsters are awesome. Second, I don't know if it executes the idea so well as your opponent is probably not going to attack it. Seems like it needs some buffing IMO, unless there's something missing.

Beiji Weng might be outclassed by Aqua Magician right now.

so far only change Stance will work with Mot but it will need more than a trap to go along with it.

for Beiji Weng vs Aqua Magican, Aqua Magician is "your opponent controls" vs "on the field" thing as it seem. Aqua magician is viable to card effects that specify general/specific monsters on the field for the appropriate target purpose, but Beiji include both even if the monster you control is mainly targeted by.