I actually based an online superhero RPG around this (homebrew system, not M&M).
A cosmic-level macro-scale version of Cordyceps was basically the settings version of Galactus, called the World Eater Strain. Almost universally infectious, it invaded an organism, first attacking the nervous system to get control of it. Then, it commands them to gather in large number, all the while producing large numbers of spores in the form of a black gunk that was extremely difficult to damage without aerosolising it. The infected gather and climb up, up and up, to the highest point on the local landscape.
They then construct a fruiting body out of as much of the local uninfected bio-matter as can be gotten a hold of (animals, plants, humans etc). This is where it diverts from the fungus, in that they next essentially build an egg, using all available bio matter (including themselves).
When the infection reached the right stage, the egg hatched into the infection vector that would leave the planet and search out and infect new ones (kind of like Galactus's Heralds). Their flight is powered by all the gathered biomatter, and in cases take-off has been known to reach relativistic speeds.
Obviously they beat it, though.