It happens with your special attacks but it only works if the opponent uses thier special attack while the timer is up. If they don't use a special they automatically go into a stun.
Only few champs have their sp1 doing more/better damage than sp2, YJ is one of them, his sp1 has a chance to power sting opponent with 3 stacks max, before the timer is over if the opponent uses sp they would suffer damage
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Read his abilities, it says exactly how it activates