Mr. Fungi, or Ms. Fungal as it eventually levels up into, is the first passive weapon on the list and it is both the return of an old classic from the series while being its own unique weapon.
Now, the Zurkon family all play different key NPC roles within Ratchet and Clank, so Insomniac created the Fungal's to replace them. Mr. Fungi is the Rift Apart take on Mr. Zurkon, a classic weapon from Ratchet and Clank which spawned a tiny robot with one goal: destroy your enemies.
The mushroom version of Mr. Zurkon is a very worthy successor, with it being just as effective as Mr. Zurkon was in previous entries thanks to it helping you take out multiple enemies without spending a bullet.
It's also hilarious listening to the little lines between Ms. Fungal and Mr. Fungi take out your enemies as a family. It's both funny and heartwarming.