If there had been 'Thunder Warriors' in the I Legion as well...
What other weapons might suit Mortarion?
Dream or Grim of Guilliman
Dream & Grim of White Scars / Primaris Jetbike / Golden Keshig & Ravenwing
The ever-evolving JoyToy Asterion Moloc
What if an 'Ascended Guilliman' model comes out?
30K Fabius
Dream of White Scars
