Fungosaurus
Walks through
EnergyFirePoison
Can't pass—
30,000 
0 
2500+
Damage taken
Resistant
80%90%90%
Neutral
100%100%100%100%100%100%
Abilities
feared
rootedLocation
Possibly at Sparkling Pools, Crystal Enigma and Monster Graveyard.
Immunity Properties
Paralysable✗
Sense Invis✓
Notes
They can appear if a Primal Pod is not dealt with in time, or during the fight against The Primal Menace if a Primal Pack Beast is not killed in 20 seconds after spawning. A Fungosaurus will despawn if it is not killed within 5 minutes of spawning.
Strategy
If they appear during the hunt you should deal with them as you would with the other creatures, just being extra careful with its Root and Fear spells. During the fight against The Primal Menace, they should not be a priority, since you will have to keep killing other Primal Pack Beasts in order to continue the fight.