this will be a post that talks about how hybrids are formed according to level
the lowest level at which a creature can get hybridized is at a lvl 4 levels higher than its base for example:
commons: lvl 5
rares: lvl 10
epics: lvl 15
so from this we can gather that a creatures hybrid can (usually) be formed at a lvl 4 levels ahead from its base.
the highest lvl a creature can get a hybrid is lvl 20
its not important for a creature to have a hybrid that is one class above it.
if you want to elaborate or add more points then you can write in the comments