Both cards have similar effects, allowing you to play cards from your graveyard
Parallels are essentially rarer versions of a characters card, with the same stats but alternate art
Jegantha, the Wellspring Lorkac: Speaking of companions, this is the less exciting but much easier to splash version of Larrus
It wants to play by the rules predictably
Rakdos is a bit different in that he can be a one-sided board wipe, but there arent that many other Devils, Demons, or Imps worth playing, and hes risky to play anyway since you could end up wiping your board and not affecting your opponent at all, so he never really took off
And with Frodo, they wanted a more heroic look, something that reflects the many years that pass between him inheriting the ring and embarking on the journey to destroy it