I like that character idea! So long as the rest of the party's on board with a character that doesn't contribute in combat, it offers a really cool option for roleplaying.
Well, to be fair, he can give advantage to attacks, and make his allies better at Athletics/Acrobatics. So, he's still contributing, just less contributing to damage.
Actually, why is he a rogue, instead of a bard who's instrument is criticism and has a bunch of spells based around criticism? He could still take 3 levels of Rogue for Mastermind if you wish.
possible spells.
Suggestion:In my true, honest, and humble opinion, you should follow me into this dark alleyway. The chances of this being an ambush are so low!
Healing Word: Oh, GET UP! My Grandmother was better at tanking than you!
Message: Psst. You suck.
Sending: Psst. you suck a lot.
Identify: And on this episode on Antiques and Magic Items Roadshow... We have this complete trash.
Bane: Wow. Just... wow... -_-
Feather Fall: Come on! My granny could make that jump!
Silence: Silence! I can't hear the sound of my beautiful voice!
Fear: Yellow-bellied coward.
Stinking Cloud: Every word out of you is just straight up crap.
Enhance Ability: A child could do this!
Hideous Laughter: These buffoons don't know to take things seriously!
Enthrall: Look at my radiance!
Detect Magic/ Counterspell: Hmm... These wizards are ridiculous. They hardly know how to cast a spell!
Modify Memory: No, that is not what happened at all! This is what happened!
Mass Suggestion: Trust me, armor is not at all the current fashion. Just take it off all that armor.
Resurrection: Come on! Death is so last season!
Glibness: Trust my critiques. They are honest and true. Robes of Flaying are completely safe and the newest fashion.
Power word kill: Oh, just die already!
True Polymorph: This is what you should look like!