Here’s an idea for a new boss infected that spawn in place of a Tank, named the Volcano. This nickname comes from how creates a substance the survivors refer to as magma/lava.
First off, he’s very large, bigger than a boomer even, but the rest of his body is also kinda big, not just his stomach. This size makes him INCREDIBLY slow, he makes up for this with his ranged attack. His skin looks similar to the Chargers arm, very rough and scabby, but also a little charred/burnt.
His actual mutation is with his stomach acid, he can digest a very wide range of materials. Following this, his behavior has changed to make him hunger for this that fit this variety, usually dirt, grass, or other plants. Unlike how most creatures digest food (to turn into waste) all the mass is held inside him, where continuous digestion super-heats the material, eventually turning some of it into small, condensed balls/lumps, roughly the size of golf balls.
His special, as many of you can guess, is that he spits/vomits this “magma” at you. But it’s trajectory would be much more like the Spitters, these large globs of heated material would be lobbed several meters, before impacting. Upon impacting, a medium sized pool, which would linger around a bit longer than spitter goo does. The “magma” would actually look very similar (to a degree) to its real world counterpart. The “stones”, small and black, would be found floating in super heated goo that would even glow bright orange at first, dimming to red as it cools (you can even see this glow within the cracks along his body).
The attack would do most of it’s damage from the initial impact on the survivors, but some of the “lava” would stay on the survivors and burn them, but when it’s on the ground it does less damage than Spitter Goo does. Due to its heat, it actually has a good chance so set most things on fire, sometimes even other infected if they don’t watch their step. But because of his already burnt up/scabby outer skin, he doesn’t catch fire, making him safe from his own attack.
Finally, upon death he would explode, leaving a MUCH bigger puddle (about the size Spitter’s spit normally makes). This blast would cause damage the same as any other explosion, hurting/killing infected if it’s realism. He actually wouldn’t have a melee attack, but rather a suicidal explosion, which would be a very powerful attack, but it’s not too OP because of his speed; you should easily be able to avoid this attack.