Groucho Glasses - Mask
Players killed no longer call out/yell similar to how the knife’s kills are silent. Can add a debuff like lower reserve ammo capacity to disincentivise camping in enclosed areas and stacking up kills.
Similar to this you could have a bandolier type item that increases reserve capacity instead. But this might be too close in functionality as Infinity.
DOOM Guy Mask/Hat
Killing people explodes them into giblets, could maybe add some doom sound effects to it aswell. Some drawback aswell would be needed since I doubt you can identify a pile of gore.
Scavenger Mask
Picking up ammo crates whilst at full reserve ammo (currently nothing happens when you walk over them) heals you for a very small amount (1-5hp). I could maybe see some maps running out of ammo very fast if this were a thing so a cap on total healing could be added?
Surgeon Mask
DNA left on corpses expires faster, preferably by a %rate rather than a flat rate to prevent it going straight to 0 at certain ranges.