The stun applies to the first ability that lands when the stun is available. If you cast Disintegrate followed by Incinerate while the stun is available and Disintegrate is in the air, the stun will apply to Incinerate.
Tibbers deals 10 / 15 / 20 (+ 10% AP) magic damage to all nearby enemies every second.
While out of combat for at least 5 seconds, Tibbers gains bonus movement speed when moving toward Annie and heals himself for 6% maximum health per second.
Tibbers enrages for 3 seconds on summon, when Pyromaniastuns an enemy champion, or when Annie dies. During this time, Tibbers becomes ghosted and gains 275% bonus attack speed and 100% bonus movement speed, the latter of which decays over the duration.
If Annie dies while Tibbers is active, he instantly heals himself for 50% missing health and targets her killer. If they are too far away from him, he targets the nearest lowest-health enemy champion instead.