Hello! First time poster seeking a bit of help...

So I am playing in a campaign at my local game shop non-AL the curse of Stradh, My character was a Kobold hunter with a tragic back story of his tribe being massacred by zombie mushrooms (Ophiocordyceps unilateralis aka Last of us Zombies). Little does he or the party know that he is actually infected by the virus but at a much slower progression and I was wondering how I could progress his slowly into a zombie possible for the Party Morality conflic later on (or just murder hobo for xp lol!).

He's class is barbarian, so I've tied the hint that he is infected to his Rage ability, whenever he finishes he beings throwing up living mushrooms (in small quantities), but aside from that I really wanted to ask the community for some creative input on how to progress his zombification and slow loss of consciousness to the mushroom.

Any ideas? I am very open to any suggestions as is my DM as well

Maybe when you raise your physical stats, you also lower your mental stats and get an extra something associated with your end form, like a Circle of Spores feature or something from the stat block of the zombie in question, chosen by your DM. 

If you actually want to go full zombie then I would use the spore servant template from the Myconid entry in the MM. Otherwise take a few levels in Circle of Spore Druid.

Here's some ideas for progression:

• Physical appearance could change slowly, over time: skin gets grayer, eyes go white, breathing becomes labored, etc.
• Occasional Intelligence and/or Wisdom saving throws, at a fairly low DC, to lose a point of Intelligence ( or Wisdom ). I'd probably do this once a day/week and whenever the Barbarian comes out of a rage. Over time, you might ramp up the DC as the infection gets stronger. If aiming to make a "playable zombie character", I might give them bonuses to strength and constitution to balance these losses.
• Require a skill check of some kind ( depending on what they're trying to do ) from other Party members to wake him up after he falls asleep. This DC would also ramp up.
• Require a Wisdom saving throw occasionally, or subject the Character to uncontrollable urges to consume certain substances. I'd make these non-normal and mushroom themed ( dirt, manure, straw, road kill, etc. ). I would not turn the zombie full on Party cannibalistic.
• Development of new abilities, like spore attacks from the Myconid Adult.
• Occasional Intelligence and/or Wisdom saving throws, at a fairly modest DC, in combat for the Player to lose control of the Character in combat, and the DM takes them over as an NPC. I'd allow them a check each round to regain control. This is another DC which would go up over time, as the infection progresses. If the  DM is planning on making the zombie a playable Character, I'd skip this one. This is mostly thrown in to really emphasize to the Party that something is wrong and it needs to be fixed.

I think that's all pretty plausible, and pretty horrible :p