I've never really understood biathalons, triathalons, decathalons, etc. Why is each one always composed of the same sports? If you had a competition composed of just biking and swimming, why wouldn't that be a biathalon, too?

I think there should be more variety in these events and you should be able to construct the triathalon of your choice, composed of individual sports that you enjoy. So if you like skiing and want to do the biathalon, but don't know which end of the rifle is which, you can swap out the rifle component with, say, discus.

Some biathalons could lead to real humor value too - consider the synchrnoized swimming / Greco-Roman wrestling biathalon.

For myself, I have created the MouserTriathalon. It starts with a full series of bowling, followed by a game of ultimate, and then you have to play 100,000 points worth of Galaga. Nina's triathalon would be similar, except the Galaga requirement would be replaced with like 8,000 games of air hockey.