Original Message

Vtoss was Vx for helicopters.   Someone (you?) said "WRONG"

If Vx is zero because it has power to climb vertically.  Then Vx is zero, but so too is Vtoss.

Vtoss is the minimum speed to effect any climb

Vx is the speed to effect the best climb gradient.

Vy is the speed to effect the best rate of climb.

Vx and Vtoss can both be zero, but not always!  You said Vx was zero since a helicopter can climb vertically.  Nonsense!