Take 1 range hero in one team (let's say morphling), and mars in other team.

Cast mars' ultimate so that the border is on top of mars (if morphling is inside, put mars slightly inside)

Now proceed to make morphling attack to mars. dipending on the animation morphling is using for his attack (which can vari from hit to hit) some attack are blocked by the ultimate, and some aren't (without either morphling or mars moving).

I feel like it should either block 100% of the time, or never block (if both heroes don't move). There's no reason for attack animation to change anything.

On top of that, it could have some other side effect with skin that change animation (dunno if there are skin that change attack animation)