Hm. Okay, so the planet you're living on has its axis flop around a lot, on the order of a million years or so.
At some points of that process, you'll have something like a normal day/night cycle, but at other points (say, when the axis lies in the plane of your orbit), that cycle will be seriously screwed up. There will be variation in insolation, but your life forms won't be adapted to it being clock-regular, like ours are.
That variation could lead to some really weird stuff - like ice ages that come and go rapidly and erratically. Whatever the day-to-day weather might be, the climates aren't what we'd consider stable on the longer term, and your life forms would have to be flexible for that.
But, you want some worlds that are deeply-seriously weird?
Larry Niven's "Known Space" books have several oddities: the Ringworld (which isn't a planet, but a construct), the Puppeteer's Kemplerer Rosette, Jinx (which is egg-shaped), and Mount Lookitthat (which is a 40-mile high plateau, the only livable land on its planet).
He also has a planet... without a planet! A torus of warm gas orbits the star. See The Integral Trees and The Smoke Ring.
If you want things with harder science, we have Robert L Forward's Rocheworld - which is two planets orbiting so closely together that they share an atmosphere, and occasionally toss an ocean back and forth between them. Forward also detailed life on the surface of a neutron star in Dragon's Egg, but that life isn't as useful for game purposes.
