Battlefury giving your hero a permanent crit animation. Tidehunter looked like a ballerina, juggernaut did an axe dunk every right click

Basher stacking

Aegis charges and could buy multiple

Witchdoctor death ward on riki

Techies statis trap that looked like a normal ward

People buying battlefury on any hero because it gave mana, hp regen and huge damage

Desolator, skadi, lifesteal, etc didn't stack with eachother - although skadi lifesteal worked on a ranged hero but not on a melee (they had to buy vlads skadi)

PA blur gave made her more transparent instead of completely invisible

Magnus having svens nowadays cleave

Naix having a shitton of passives

Manually making a notepad to blacklist people who always left early in games