As of ways of forcing advantage, I think the only ones to work are:
- another character or rogue standing already next to caster
- faerie fire(rogue cant cast it)
- entangle(again, i dont know of ways for rogue alone to get it)
there is new ointment poison like type that gives you advantage on attacks, i think it would work with spells
anyway, i have grave news. Thief subclass, once finally reaches umd... cant use scrolls!
im still processing my disappointment, spent whole new campaign up to this point crafting fireballs.
now for good things. Since I took my lost valley save, Ive gotten access to some magical items vomit(although i should have bought warlock and bard items too).
There are 3 items that perform very well.
- horn of blasting -> 5d6, 10 uses of sound cone, requires tuning
- pipes of haunting -> 3 uses of fear cone, possibly bugged, can use it pre lvl13 since its not bard tagged and does not require tuning. My party got paladin so i dont care about friendly fire. Jump next to enemies and they will run forcing reaction attacks. Use ointment mentioned above and you force 'extra' sneak attack(although I didnt actually test yet that it works)
- wand of lightning bolts -> 8d6, 7 uses, can recharge fully within 1 day, requires tuning.
So yeah, thief can add quite a bit of extra damage on top of standard sneak attack.
looking up there is respite flute that would provide some nice heals and extra hp