When you fight the king Titan, fight the gamma version with 16H and 16M gigas (atleast 70+ gigas) and maybe a good mech and no titans, then with the beta use the Titans and the same gigas (breed more if you lost most of them) and don't tame the desert Titan because its health is sh*t only tame the ice and forest Titans because they have over half mill health and do a ton of damage, then the alpha, breed more of those gigas up to 80+, you need 4 Mechs to form the megamech, once you formed the mech after summoning the alpha king titan order everything to attack the king titan (you may need to get off the mech to get everthing to fight it) and yes help your Titans out, hope this will help you all if you're planning on fight him, remember to fight all versions and fight the beta to get the megamech object