All items for melee builds are pretty simple (more damage,etc.) i think items that would add effects to melees would be a great addition. For example an item that gives a player knockback when he punches someone.
That would be broken on Viscous, and would be counter-intiutive. Would sabotage your team and yourself more.
I could suggest an item that gives you 0.5 seconds of invulnerability upon a heavy melee punch hit, where you can't take any damage, with light giving 15% damage reduction (works against pure damage also) for 1 second. Upon a kill, become completely invisible for 2 seconds, can only be seen via effects/abilities/gunshots coming from them. Not even getting upclose reveals them. No cooldowns.
Or how about hitting a light melee gives you 60% fire rate for 2.5 seconds?
Goes on cooldown for 10 seconds.
Passively:
Could also provide move speed, bullet resist, and on lower hp (40%) gain:
More bullet resist
Faster light melee speed.
Think a bullet version of frenzy, but juices up light melee/gun fusion (anti bullet), instead of dps kiting (anti spirit).
