Channel is a spell made by Blizzard that was strictly used for triggered abilities (Custom abilities and spells that use triggers to get their effect). Therefore, Channel doesn't do anything when cast, but has more customization options than you could think of.
Use channel to make custom abilities and spells that need a trigger.
We will first want to go to the Ability Editor inside the Object Editor, and make a new ability. Look through the list under 'Hero' and you should come across an ability called 'Channel'.
The key parts of Channel
We have many more options in Channel than other abilities, here is the list of the most commonly used and key options:
Art duration: Art Duration is the Duration of the special effect you attached to Channel when the unit starts casting the ability.
Base Order ID: The Base Order ID is the ID of the spell. In Channel, if we change it, it actually HAS an effect. Changing the ID can help because if a hero has two abilities based off the same ability, their IDs get messed up and he'll try to cast both. Changing this in Channel will change it's ID to something different, meaning you can have multiple Channels on the same
Disable Other Abilities: The Disable Other Abilities feature will turn off the casting unit's other abilities during the Casting time and Duration.
Follow Through Time: Follow Through Time can determine whether or not the ability is channeling or not. If we want it to be channeling, set the Follow Through Time to he Duration of the spell and remember to set Disable Other Abilities to false.
Options: Options is very important. If you do not check the box that sais 'Visible' within Options, that means you cannot see or cast the ability when it's on a unit. This is the only one you need to worry about in Options for now.
~Targeting Image: This determines if the spell has the area of effect image like other abilities.
~Physical Spell: This determines whether or not the spell goes through Magic Immunity or not. If this option is checked, that means you will get no error when trying to cast it on units with the Anti-Magic Shell buff or who are magic immune.
~Universal Spell: This means it goes through anything. This option really isn't necessary unless your using stricter JASS methods, checking the options if it is Universal or not. But I will not get into that.
~Unique Cast: Another strict JASS method. You will most likely never use this, because it's more for 'tallying', and isn't used by the spell.
Target Type: Target Type is the type of target you select. If you want it to be instant meaning no target, if you target a unit,
ground, or both.
Area of Effect: Area of Effect is the same in all abilities, and it's the area of the effect of the ability. Mainly used for the targeting image (You HAVE TO have 'Targeting Image' selected under the Options menu) and for JASS methods. Set the area of effect to 0 if you want the normal, no-area of effect targeting image.
Buffs: In the Buff Editor, you can make a new buff for Channel. Buffs show up on the unit under 'Status' when you select them, and have a small icon and a description of the effect they are under.
Casting Range: Casting Range is the range of the ability.
Casting Time: Casting Time determines how long of a wait there is before executing the effect. If the Casting Time is set to one second, the animation will play, and it will wait until then to execute the effect.
Cooldown: Cooldown determines the length of time it takes before the player can cast that ability again.
Duration: Duration is the length of time for the effect. If the effect is area of effect damage over time, this will determine how long that lasts.
Effect: Effect is strictly the art that plays when the ability is cast. If you have an effect model you'd like to play during the ability, you'd make a new Effect in the Buff Editor and add it to the ability.
Mana Cost: Mana Cost is the amount of mana it takes to cast the ability.
Targets Allowed: Targets Allowed can be a little tricky. This determines who you can target when you select a unit target. If you put it to dead units, it can ONLY be cast upon dead units. Same with ground and air. So, if you want it to be cast upon air and ground units, you'd select both. If you put it for Ground, air, and hero, then it can only be cast upon flying or ground heroes. Selecting ground and air will suffice to cast upon heroes as well.
Tips of the trade
~When you want to select when a unit casts the ability, you want to use the action "Unit - Generic unit event; Unit - A unit begins casting an ability" or "Unit - A unit starts the effect of an ability". Be careful which event you pick, because if you put it to "begins casting an ability", the player can quickly cancel the spell but get the effect. This can be avoided by setting the event to "Starts the effect of an ability".
~When we want to determine which spell is being cast, use the Condition
"Ability Comparison; (Ability being cast) Equal to your ability". When we want to determine what level the ability is, you can use a quick if/then/else with the condition being "Integer Comparison; Level of ability for unit".