Multiple Arcane Marks

[Sado]

Can two magic-users cast Arcane Mark on the same object? If so, what happens if they both try to cast Instant Summons on it at the same time?

 

[UltimaGabe]

It'd be pretty hard to get them to cast the spell at the exact same moment, but if they somehow managed to do it, I guess roll a 50/50 chance of which one it would go to. The other would get the same result as if it were in a creature's possession, as per the spell.

Edit: Maybe an opposed caster level check?

 

[Hypersmurf]

It'd be pretty hard to get them to cast the spell at the exact same moment...

Yeah. They roll initiative. If it's a tie, the person with the higher modifier wins. If that's a tie, you reroll until you get a winner.

Then the spells resolve in order, so the first caster gets it, and then the second caster learns the identity and location of the first caster.

-Hyp.