A term given to any character in a video game who inexplicably dies by simply touching the water despite them being able to accomplish many other amazing feats.
The name is taken from the character Altair in Assassin's Creed who, despite being a trained assassin who can leap from 50 foot towers into hay and survive, cannot swim and dies from going to deep into the water.
Often used as a cheap way to stop players accessing certain areas by game developers, similar to the invisible wall.
John Marston (Red Dead Redemption) - Brilliant with a gun, managed to take on entire gangs and the Mexican army by himself, cannot swim and dies in waist deep water - Altair syndrome
Eddie Riggs (Brutal Legend) - Guitar playing, axe wielding, half demon roadie who lead an army to defeat an demon emperor of a heavy metal based land. Similar problem to John Marston - Altair Syndrome
Batman (Arkham City) - He's batman, do I even need to explain this - Altair syndrome