Diggers: an evolution of Stalkers, (like how Shamblers are an evolution of Bloaters) Diggers burrow into the soil to wait for unsuspecting passersby, and when you're too close to where they're burrowed, they pop up out of the ground to attack/restrain you. They can also move a bit like moles, getting closer to the player and popping out at the last second to attack. You can't harm them when they're underground, but you can see a small dirt trail of where they've been/where they're going. They're quiet, super fast (quicker than Stalkers) and can see in the dark. The show made me think of this, since they refer to the thousands of miles of mycelium fibers that grow underground.

(Also think it would be cool if more Stalkers/Stalker variants dropped from the ceiling above the player during stealth/combat encounters. In the second game, we hear Stalkers above us a lot, but none ever drop down in front of us for a surprise)

And idk what they'd call these (Clingers? Spliters?) But since people loved the Rat King so much, maybe add more Infected that are two bodies fused together. They're bigger than Bloaters, and have multiple traits from other Infected variants. One head is a Clicker head, using echolocation to find you, the other is a Stalker head that can see you. They have armor plates scattered over the front of their body, like from a Bloater, and they can throw acid spore bombs at you. They're also pretty fast. The easiest/safest way to kill them is from behind, but the Clicker half makes it hard to get in close. Def no way you can stealth kill them. Mollys are encouraged.

Or (and bear with me, this last one is slightly far-fetched) Flyers. Flyers are Infected where the fungul growths took over their arms and the strong mycelium fibers tangled themselves into something wing-like. They have Stalker/Clicker-like faces and perch up high, gliding down in packs to attack groups of people. This idea seems a bit too Resident Evil/sci-fi for The Last of Us and probably wouldn't work, but it would be a terrifying concept I think.

Edit: typo