The IItemInteractionForEntity function can be added to an Item and will be triggered when a player right clicks on an entity with the item.

It might be required for you to import the package if you encounter any issues, so better be safe than sorry and add the import.
import mods.contenttweaker.IItemInteractionForEntity;

The IItemInteractionForEntity function is a function with the following parameters:

• IMutableItemStack itemStack → The item that was used
• ICTPlayer player → The player using the item
• IEntityLivingBase target → The entity the item was used on
• String hand → Either "OFF_HAND" or "MAIN_HAND"

The function needs to return either true or false

ZenScript
 Copy
#loader contenttweaker

import mods.contenttweaker.VanillaFactory;
import mods.contenttweaker.Item;
import mods.contenttweaker.IItemInteractionForEntity;
import crafttweaker.entity.IEntityLivingBase;

var sheep_remover = VanillaFactory.createItem("sheep_remover");
sheep_remover.itemInteractionForEntity = function(stack, player, target, hand) {
    if target.definition.id == "minecraft:sheep" {
        target.removeFromWorld();
        stack.shrink(1);
        return true;
    }
    return false;
};
sheep_remover.register();