Combat
What Does Stun Stop a Unit From Doing?
Stun removes a unit's contribution to combat damage. It does not switch the whole unit off.
RiftPal explanation · Answer first
The short answer
Think of Stun as removing a unit's contribution to combat damage, not switching the whole unit off. The unit stays on the board and stays involved in combat.
Leave out its MightMight represents both how much Combat Damage a unit can contribute and how much marked Damage it can normally take before being killed.View in Glossary when calculating its side's combat damage. Its Might has not changed, though: it still takes damage and is no easier to kill just because it is stunned.
RiftPal explanation
How it works
Stun changes what the unit contributes to combat damage. It does not remove the unit from combat or reduce its Might to zero. To work out how much damage kills it, use its full current Might as normal.
Stun and ExhaustTo Exhaust something, turn it sideways to show that it has been used for an action or cost that requires it to Exhaust.View in Glossary are separate. A stunned unit can still be ReadyReady means a card or rune is available to be used for something that requires it to Exhaust. Ready objects are kept upright.View in Glossary . Because Stun has not switched the unit off, it can still make a Standard MoveA Standard Move is the normal way a unit moves between its Base and a Battlefield.View in Glossary if it can pay the Exhaust cost and the normal movement timing and restrictions allow it.
Its abilities are not automatically disabled either. You still follow their normal timing, costs and restrictions. Stun itself adds no extra ban on using them.
Stun normally lasts until the end of the current turn, whoever's turn it is. Ending a combat does not remove it. If the unit leaves the board for a hand, trash or another non-board zone, it loses the stunned status.
An effect can choose an already-stunned unit if it is otherwise a legal choice, but the unit is not stunned again. That means it does not trigger an ability that needs you to stun a unit.
In practice
Example
Card example
Noxus Hopeful
You have two units in combat: one with 4 MightMight represents both how much Combat Damage a unit can contribute and how much marked Damage it can normally take before being killed.View in Glossary and one with 2 Might. Your opponent stuns the 4-Might unit before combat damage. With no other effects changing damage, your side now has 2 combat damage to assign.
The stunned unit is still in the combat and can still take damage. It still has 4 Might, so if it had no damage already marked on it, it would normally need 4 damage to be killed. Stun has removed its damage contribution, not made it a 0-Might unit.
Unit
Noxus Hopeful
[Legion] — I cost [Energy 2] less. (Get the effect if you've played another card this turn.)