In the Trails there is a Hero that casts Clone and unlike all the other summoned creatures it doesn't lose life when the hero is attacked or drained of life. What is the weakness of the cloned creature?
Clones are not supposed to take the damage deal to the hero. Only heroes that summons their own creature (not cloning) like Predator, Dragon Rider, Berserker, Deathmort and Stormkallar. Those creatures have the ability of take the damage dealt to the hero, clones do not have that ability.
To defeat them you just need to kill them as if they were another creature.