Symbiote

It suddenly jumps onto you. You feel a searing pain as it latches onto your arm, but in an instant it is gone.

...? Where did it go?

Along your travels, you stumble upon a dark, amorphous polyp. You can sense that it is very old, and very evil.

Approach...

You torch the dark polyp. As it screeches and burns into ashes, your head pulses painfully but you manage not to faint.
What was that thing?