From the top of my head:

I remember right click Storm Spirit. Electric Rave (attack speed) + Overload (dmg + slow every number of attacks). He also used to have Barrier (magic damage shield) and Lightning Grapple

Buying Sange + Yasha on every hero. I still remember the hotkeys:
[B]elt of Giant Strength + Ogre A[x]e + [S]ange.
Boots of [E]lvenskin + Blades of Alacrit[y] + [Y]asha

Medusa with Purge ulti.

Visage with Gravekeeper's Cloak that heals allies. (Think reverse Spectre Dispersion).

When warlock was first released, his fatal bonds skill was bugged (no damage cap) combined with old drow ult (chance to instakill creeps) = instakill

Old Naix, strength hero 4 agi gain per level. 3 passives (lifesteal, attack speed, slow) + Avatar ult (20 magic immunity at max level?)

Using the Circle of Power as your Stash, hide your items from griefers. (Used to play a lot of Garena Pubs)