Elves would be granted a callable inherent ability called 'superiority' which would allow them to (offensively) reduce a target's intelligence: I'd say by (Elf-char-intel MINUS Target-char-intel) DIVIDED by two. On a giant, this could easily be 4, but on a dark-elf it would likely not be more than 1 without other external factors involved.

The elves are of godly intelligence and are an incredibly overbearing race, I think that this would give them a cool RP attack which would not unbalance things terribly while still being useful for certain situations. If you want to be mean, maybe let there be a primary roll to see whether the ability would be considered offensive or not. This ability can not be allowed to stack on a target, or be used too frequently by an elf. Consider.

Glad to see the contests back in force,
-HT