Quantum tunnelling cyborg
We all know MC is a special guy, but did you know he's able to pass through solid metal walls? I found this out in the rockslide survivor area one day when I was inside the lifeboat dealing death with a sniper rifle. "This might be good cover" I thought. But then I hit the reload button and suddenly found myself transported outside, sitting in the driving seat of my Warthog which had slid to a stop alongside. Of course, it was just that annoying old reload glitch again, i.e. hitting reload when you're near the hog, causing you to unintentionally board the darned thing. Apparently there's no account taken of whether there's a metal wall in the way. Anyway, so much for my cover!
Update: Many years later, I used this boarding method to make a quick escape from an explosive situation. See BCM314 around 6:14.