Stuck at the "Kill the Star Parasite with its own crystals" level.
( The Swamp Queen is observing up on the ledge. )
The Journal mentions on the roof.
But the level introduction video showed the Star Parasite as being down.
( the Left Alt key is not showing anything. )

Where is the Star Parasite?

Probably a little late but anyways:

AFAIR the "Star Parasite" is that big, purple-isch, rotating, planet-like, broken thing.
You can only harm it by shooting those red shells with the dwarf that, well, shoots shells (special ability, "R"-Key).
However, you have to collect these special red shells first, they are appearing somewhere on the map.
Once you shot at the Star Parasite (just aim as normal, it will highlight orange), the next shell will appear.
So the challenge is, to defeat incoming enemies while collecting shells and aiming/shooting them at the star.
It takes about maybe 5 to 8 hits to take it down.