MycoRelic upgrades, body parts and elemental powers
Official pages say you start in a decrepit, moldy frame and scavenge parts to replace it, raising stamina, frame integrity and fungal magic. You also infuse yourself with elemental powers found in fungi — fire, healing water and a spiritual essence — and can combine those effects. The 1.0 notes describe a Truffle Smith who upgrades gear rarity and can re-roll weapon perks.
The robotic body
Both the official website and Steam describe the same starting point: a worn, moldy frame that you replace as you find parts. The stated goals are surviving the environment, backing up a combat style, and strengthening elemental effects. Stamina, the integrity of the frame, and the strength of fungal magic are the three upgrades named in that copy. A full list of body parts is not on the store page. The 1.0 patch does name some additions, including a T2 Ghost Frame body-part set and Torquake arms with a perk that boosts unarmed damage.
Elemental infusions
Official feature text talks about attuning to elemental power inside fungi and combining effects. Fire is described as a way to burn enemies and open a path through barricades. Healing water is described as a way to restore allies and block roaring flames. A third axis is called the spiritual essence of the world, used to empower allies. The 1.0 notes go into spirit-ability changes (Spirit Ball, Spirit Empower and related perks), which shows that spirit is a worked-out combat resource, but they are patch notes, not a complete skill tree.
Truffle Smith and rarity
An earlier Early Access post introduced the Truffle Smith and items called geotruffles, used to raise rarity (and stats) one step at a time. The 1.0 notes say you can now re-roll weapon perks at the Truffle Smith, that white items had been upgrading beyond intended values (now fixed), and that the smith could delete items when asked to upgrade junk (also fixed). The Gun Club can now be upgraded. Exact geotruffle costs per tier are not copied here from older notes, because later patches may have changed them and a current official cost table was not published on the 1.0 post.
Caster-style M-Drives, a bracelet that raises equip load, and several miniboss unique items are also named in the 1.0 notes. How to obtain each one, and what every perk does, is not fully documented on the public store pages.