Animation cancel is an oversight in Battleheart which can be used as a very helpful battle tactic. Similar to animation cancel in other strategy games like Warcraft and Dota, animation cancel is basically a way to 'cancel' the action of a character's attack/heal, allowing it to perform the next attack/heal without any delay at all.
This allows many characters to have increased healing/attack speed. It will allow the Cleric to heal up to 5 times more than its normal healing speed, as well as to increase the attack/boost speed of Wizard/Witch/Ranger/Bard up to 5 times as well, rendering such attack speed items useless.
The animation cancel is best seen with the Wizard/Witch. Have the wizard attack a target, and immediately when the wizard raises its staff to attack, move the wizard ever so slightly and have it retarget the monsters immediately after the move command (do not wait for the wizard to actually move to the selected location). If done properly, the wizard will drop the action 'delay' and start raising his staff immediately again. Repeat, and you will have an attack speed of up to 8 times the normal attack speed.
Animation cancelling Cleric are very useful. It will allow enough healing to be able to beat ALL levels without the need of a tank (or even any melee character), allowing you to have maximum damage output (animation cancel all the ranged classes).
Animation cancelling for melee characters are not very effective, but they can be done if you have really fast APM. It will only work on non-tank melees, as tank melee will take aggro of the monsters. First, make sure the monster is NOT attacking the melee character you want to animation cancel with (thus why tank melees cannot be animation cancelled). Move the target of the monsters slightly up or down, but NOT sideways or diagonally. This will make the monster move in the same direction as well, and now you can do animation cancel with the melee attacking it (by moving the melee character to the same 'line' as the monster). This can cause up to 4x faster attack speed.