Items that get exponentially stronger when stacked by your team

What items are the strongest when multiple teammates stack the item at once?

The first I can think of is Siphon bullets, if all 6 teammates shoot an enemy with Siphon and then get the kill then the enemy will lose 330 health which is huge and I can image some cheese snowball strats where >1000 worth of health can be Siphoned from one enemy.

I can also think of Knockdown, the item is cheap and the stun duration is short which means it's harder to accidentally overlap debuffs like with Curse or Silence Glyph.

The last I can think of is Health Nova. The regen scales with allies affected and is casted over time. This means if multiple teammates pop it at once you can most likely sustain through large AOE attacks like Haze ult or Lash combo.