Im making this guide because so many people miss the point of interrupting.
It is one of the most important skills in the game, so here is some information on it.
What spells have interrupting capabilities?
Torch Bearer: Frost Nova, Deep Freeze
Unclean Beast: Foul Grasp
Regulus: Dead Eye(doesnt really count, but added anyway)
Rook: Boulder Roll
Sedna: Pounce, silence
Lord Erebus: Mass charm
Conclusion: anything with a stun is an interrupt.
What spells can i interrupt?
You have to LOOK for their animations of them casting the spell. some are more difficult to see than others.
I have not listed several spells because they are "instant" or 0.3 sec cast or lower, or others which i dont think is important (summon shamblers, horn of yeti, uproot).
Against Torch Bearer:
Fireball, spins his staff in a forward direction
Frost Nova, ice surges towards his feet
Fire Nova, rises quickly into the air whilst in flames
Circle of Fire, spins his staff in an anticlockwise direction around his body(like hes trying to be a helicopter)
Against Unclean Beast:
Foul Grasp, obvious
Any ministun will stop this channeling effect from working.
Mines, his arm coils underneath his bow and throws them.
Hammer Slam, obvious
Structural transfer, obvious, any ministun will stop this channeling effect from working
Boulder Roll, his left arm touches the ground, and he kneels down
Surge of Faith, has a clear shield around him when casting
Interrupting her spells are extremely difficult. Personally i cannot tell when she is casting.
Heal, sila just crouches, the easiest way to interrupt this spell is when they are running away and they stop quickly to heal.
Against Lord Erebus:
Mass Charm, obvious
Item and teleport usage:
All items (except for teleport/universal gadget) have the same animation! all demigods do a scratching movement with their hands.
Flag lock item:
When using a potion, you will not turn around at all. These same animations are used for all items (except teleport/universal gadget).
It will make you face the location you are going to teleport to.
Note, this same animation is used for the favor item Amulet of Teleportation.
A universal gadget:
When using a universal gadget, they will turn and face the location nearest to where you clicked on yourself, or face the demigod you are about to cast it on.
Readying yourself for interrupting:
What i normally do is chase with auto attack and have my interrupting spell(e.g. pounce) ready so all i have to do is left click on my target. Like below(this is just an example of how to do it):
Unfortunately its abit hard to see my mouse hovering over QoT with my pounce ready.
Other Finer Points to Interrupting:
If you use an interrupt on a target who is ALREADY stunned, it will end the stun. if your team mate foul grasps an enemy, a mini-stun/shield from either allied or enemy sides will cancel the channeling.
The only time you cause the cool down timer to 'tick off' is when you actually interrupt the spell in mid cast.(thanks to zechnophobe)
If they are still moving into position to use an ability, or hadn't started casting yet, you will simply prevent them from casting it until the end of the stun.The command will still be queued up however, so they will try to do the ability immediately after the stun wears off. (thanks to zechnophobe)
Think! Count in your head, if you know a spells cooldown time, they are probably going to be using it as soon as the cooldown timer finishes.(thanks to Itchydustbin)
You can interrupt potions, teleport scrolls and favor items.
Deathbringer can be used as an interrupt.
Dont always use your interrupt for damage, stopping a teleport/potion can be more effective than just using it for damage.
I hope you learnt abit about interrupting. if there is anything you would like to add just let me know and ill put it up here.
Make sure you interrupt!