How do i make Custom Attacks Animations for a boss

Hello Everyone, as said in the title i wanna do Custom Animated Attacks for a boss that im doing but i really dont know exactly how to do it. Im using Geckolib to do the attacks but to get that into the game is very hard to me right now, example, i wanna do an melee attack ( The Normal Attack ) but i also wanna do that the boss do 2 more differents attacks, i need help in how to make those attacks combine into the mob and also need how to do the cooldown, any help is aprecciated.