Was going to have Flying (Red has Dragons after all) but not too sure that is best fit for but what else is there?

Power and Toughness switching pops up in both colors. Spell redirection does too, as in "target creature you control becomes the target of target spell with a single target". Target target target target. You could also do something like "Target creature you control is a 3/1 red and blue elemental until end of turn."

­Cromat had a similar problem. It ended up using flying for this colour-pair.

But I also like "switch target creature's power or toughness".