Araragi, Peony.
Araragi - Ex-vampire driven to try to help others, when not being an emo slowpoke sloth.
Powers: Araragi, being an ex-vampire, has retained some of their powers. Bakemonogatari is tight-lipped but we know for certain that he can heal really really damn fast and that he's got a limited ability to see curses, spirits, auras of evil or weird, and other such supernatural phenomena. He's really not too bad in a fight, either, but he's no more powerful than most humans unless he lets a vampire drink his blood, which will leave him woozy but powered up. If he drinks blood his vision and senses get sharper.
Possible Pings: Ex-Vampire, 'oddity', a thing of unnature. Has two bitemarks on his neck; rubs these when worried or thinking.
So, how evil?: Not evil, just lazy. Say the magic words 'please help me' and you'll have a dramatically stalwart ally, not that he's able to actively do much.
Perceptive Powers: Able to see supernatural effects. Less but still somewhat able to see supernatural creatures. Possibly has zoom vision if he's drunk lately.
Can I mess with them/read their mind?: Yes. You'll get a lot of the above information, together with a deep self-loathing, a rather analytical narrative mind, and some dere for Senjougahara.
Can I kill them?: You can try, but nothing's managed it in canon yet up to and including tearing out portions of intestines. Ask me.
Can I do something more specific, like shapeshift/body hijack/steal powers?: Ask me!
Can I annoy them/earnestly attempt to interfere with their life?: Oh hell yes. Araragi's life is made to be pain. Being cheerful at him will be especially irritating. Vampires are eagerly encouraged to seek him out for a spot of lunch as he is basically a walking blood bank.
Can I attempt to malevolently harm their relationships or happiness?: You can certainly try, though you'd be hard pressed to do any better than Araragi himself. Senjougahara is his confirmed girlfriend, and they've stuck together through thick and thin thus far.
What about meta powers?: ... not... quite breaking the fourth wall as relates to himself. Araragi comes from a SHAFT series and certainly has a dramatic amount of knowledge on characters common and obscure - a large part of the some episodes is throwing references back and forth in a game of one-upmanship with the loli. Araragi and Senjougahara have an involved conversation joking about their voice actors but it remains just this side of joking. Being SHAFT, however, in camp all bets are off.
Anything else?: Araragi narrates quite often in the series, I show this with subject line text. His 'red', 'white' and 'black' icons serve a purpose, sort of, but are mostly included for my own artsy ridiculousness.
Peony - Moron emperor with a heart of gold surrounded by sense.
Powers: Beyond some simple magic and some decidedly mortal fighting power, Peony's main claim to fame is a dramatic quantity of emperor-like common sense when needed.
Possible Pings: Not much of any.
So, how evil?: Mischievous. Not evil at all.
Perceptive Powers: Common sense and worldly-wise-ness, together with a large amount of camp first-hand experience.
Can I mess with them/read their mind?: Yes! Peony's generally pretty open and makes no real secret about what he's thinking.
Can I kill them?: Nnnnnot really unless for humour and gag purposes. Ask me.
Can I do something more specific, like shapeshift/body hijack/steal powers?: Probably! Ask me.
Can I annoy them/earnestly attempt to interfere with their life?: You can try, but Peony'll give as good as he gets.
Can I attempt to malevolently harm their relationships or happiness?: ... you can try though be prepared for Peony to pull some nasty tricks. Becky is his defacto daughter.
What about meta powers?: Having spent years in camp Peony's very blaze about this whole affair. He assumes most people are from a canon, and has played his own. He doesn't actively fourth wall break, but does meta a lot.
Anything else?: He's usually got some rappigs nearby. These guys are invincible - they go flying when hurt, instead - and otherwise pretty much completely benign.