Easily killable with a wyvern. Lightning and poison easiest down to longer range in attack. Just hover above and light it up :) killed my first today and it didn't touch me once. Just remember to watch stamina ;)
Oh, you think titans are hard to kill on pc and console? Try mobile. They have around a 10x resistance to bullets and your creatures. The only things that do full damage to titans are compound bows and explosives.