Ninja: Walk in shadow.

[YanderePrincess]

I threw Arcanist in there because it is possible that skills like Miasma or Bio could become cross class even if they aren't today. Those skills actually make a lot of sense for Rogue and Ninja.

Conceptually, maybe, but in practicality, they don't. They're int-based spells. Rog/Nin is a melee dps, most likely str-based, possibly dex-based. Just like if you could cross-classed Aero or Blizzard II onto a Lancer or Pugilist, you won't get any significant damage out of it.