What do you think is the best class combination for a build focussed on Heart of Theodin Marcell?
Apostate or Reaper, I think.
did they have any aether synergy?
Apostate - surely, especially in Bonmonger set.
Reaper - slightly less but still not bad.
Apostate with Bonemonger set,yup.
Reaper with aether RR conduit is decent.
One can used it in classes like Death Knight,Batrlemage,Opressor,Spellbinder or even Defiler,but usually it’s not gonna be good.If you have Auto attack replacer,Mindwarp is better.
wow really nice set, do u have any good bonemonger build?
Have you checked the compendium?
this one is most interesting imo 
spellbinder!
