Hmm, hard to say... In terms of design, I do love Marta's, she's cute and her fang is the best (dear character designers: please give ALL your characters at least one tiny fang, it's the best). In terms of everything else... Honestly pretty fond of Alice. I love her sadistic assholery, she's just a terrible person but has such a good time being one. There's something really fun about that sort of character who knows they're awful and owns it. (And yet, even so, still has a sympathetic background)
4. favorite part of the game?
...That one skit where Emil's talking to himself and thinking about how Regal killed the one he loved and wondering if he could do the same when the time comes to fight Richter and then gets himself all flustered about "[...] I'm not in love with Richter or anything. I mean, it's not like that! Not that I don't like him or anything. Actually, I like him a lot but..."
It's just so funny. Whether you ship it or not it's just silly and cute and Emil's a goof and I love it. His "I don't even know what I'm thinking anymore..." plays in my head every single time I confuse myself.
5. opinion on the mascot character (if applicable)?
Hm, who would that be? There really isn't a mascot in the more traditional sense, but I'd probably stuff Tenebie into that role, and I do love the darkness-obsessed old man. XD He's fun, and I especially forever laugh about how he basically stuffed his boss into a tube top with a butt cape Just Because He could.
Though if we expand beyond just the game itself and take from the OnR manga, I'd guess Pontus the Polwigle gets that role and I also very much adore Pontus XD