How does Terrorblade's Sunder ability work?

Question

How does exactly Terrorblade's Sunder ability works?

To be precise I would like to know what will happen if Terrorblade has X% of its health and enemy hero has Y% and Terrorblade casts his ability on the enemy? For all possible X and Y values.

The reason I am asking is that I do not quite understand the limitations of the ability.

It is said in gamepedia that:

1. Some hit points must remain.
2. Minimum Health: 25/20/15%

Does it mean that after casting the ability on other hero the hero will have at least 25/20/15% of health left? What will be health of Terrorblade in this case?
Or does it mean that you can not cast the ability when Terrorblade has less than 25/20/15% health? Or something else?

Answer 1

This is not a condition on being able to cast the ability. It will always work.

After Sunder Terrorblade will have as much % of his health as the target had, and vice versa.

But afterwards, another rule is applied to both of the participants of Sunder. If they have less than 25% of their health, it will be raised up to that percentage.

For example, if a full-health Terrorblade Sunders someone who has 1 HP, Terrorblade's health will be set to 25% of his own max health, and the other guy will get full health. Works exactly the same vice-versa.

And if both participants of Sunder have 1 HP, they will both have their health set to 25%.

There is also this trick: if Terrorblade is at extremely low health, he can make an illusion and Sunder it to get 25% of his max health.

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And here is some Python programming language code that simulates Sunder with Terrorblade having health1 out of max1 health and the target having health2/max2:

health1, health2 = max1*health2/max2, max2*health1/max1

if health1 < 0.25*max1:
    health1 = 0.25*max1
if health2 < 0.25*max2:
    health2 = 0.25*max2