They're surprisingly adventurous critters, even when hostless, but when they're riding around on a human's head, they are fearless. Dangerous in a fight, they rarely stay in one place, leaping from head to head in the fray, staying one enemy's sword, misdirecting an arrow on the next, interrupting spells and generally busting heads.
They're very fond of humans and never have understood the distrust they suffer, although they're also notoriously... unsentimental about their hosts. You might say they're fond of humans in the same sense humans are fond of particularly ornate wrenches.
Another Weird Hero, I remember reading a Brockway article and loved this idea of heroes that possess their enemies. In this case, imagining the interaction between a human party and a Jelly Tyrant's various hosts. The idea is that the Tyrant swaps hosts periodically throughout the campaign, to the discomfit of his allies. I don't know, I'm working on it.