I would pick the ability to offer 2 for 1 cinema tickets by threatening Arnold Schwarzenegger that Meerkats have.
The ability to lick myself!
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"This will be a fight against overwhelming odds from which survival cannot be expected. We will do what damage we can."
-- Capt. Copeland
The Naked mole rat's abillty of bieing able to resist everything those naked little freaks are tough as nails.
Narwhals. Because they are so awesome.
"There is a pervasive myth that making content hard will induce players to rise to the occasion. We find the opposite. " -- Ghostcrawler
"The bit about hardcore players not always caring about the long term interests of the game is spot on." -- Ghostcrawler
"Do you want a game with no casuals so about 500 players?"
I prefer to keep the set of abilities I have already, it seems well rounded and I do not think there is a single ability I would exchange it for.
I already have several abilities of a mammal. :P