Gira Parasite

The Gira is a parasitic plant that proliferates by embedding itself in the body of a host, growing roots through the nervous system to the brain where it stimulates rapid muscle and bone growth. It also increases aggression and causes other unexpected mutations. When the host is large enough, the Gira spreads seeds from its new higher vantage point to drift down on other unsuspecting creatures.

In large numbers the gira causes massive bursts of growth, tearing skin and muscle and significantly shortening the host's lifespan. However, in cases where only a few Gira attach to a host and live with it throughout its life, the relationship becomes almost symbiotic- with the Gira's influence allowing the host to slowly grow beyond the standard limits of their species.
The Gira's main host is the genial Affe, a slow moving, thick skinned animal that hardly notices the plant growing into its skull.
Other animals can also be affected, though more rarely.