I'm currently playing through the game on each class, and I will be sharing my thoughts with regard to character builds. Today we will be looking at the Mystic class, which is a spellcaster with some healing capabilities. Their dedicated weapons are scepters (one-handed) and bells (two-handed).
To become a Mystic, you must reach level 10 as a Novice and obtain the quest "Disciple of Magic" from Angela, then read the tome she gives. This cannot be undone, so make sure this is the class you want.

I've decided to introduce a 5-point grading system for each skill to give a better idea of what I think of each one. A 1 (●○○○○) means it's almost never worth taking (in my opinion), and a 5 (●●●●●) means it's almost always worth taking ((in my opinion)).

I will be updating these guides as my opinions and the game itself changes. If you have any criticisms or thoughts of your own, please feel free to share them.

In games with limited available slots for active abilities, I find that there's one primary rule you need to follow: Use your abilities, or lose them. If you find that you aren't using an ability often, it's almost always better to swap it out for another ability you will get more use out of.

Experiment. Try different stuff. Learn what you like, and what you don't like.

Your choice of race is largely inconsequential as it only dictates what skill you start with permanently unlocked in your book. All racial skills are able to be learned via scrolls.

I picked Kubold, mainly because I like Kobolds, but also for their Alacrity skill which is good for casters.

As a Mystic, your primary stat is mind, which is what all of your class skills scale off of. So, you should primarily invest points there.

I highly recommend investing at least some points in vitality so that you don't get flattened by a sneeze or a mere gust of wind. I personally went with 2 points in mind, one in vitality every stat bump, but your mileage will vary. Go with however much you're comfortable with.

I do not recommend investing points in dex just for the crit chance, as you can get a decent amount of crit from gear alone.

●●●●● Fluxbolt - Bread and butter single target damage spell. I almost always take this. Not as great on multiple targets, but can still hit multiple targets if they're tightly packed together.

●○○○○ Fluxclaw - I don't really get this one. Since the cooldown increase for Fluxbolt I guess you could use it as a filler but it does less damage than your weapons (which you can do at range, for free), so it feels like a waste of MP. And skill points.

●●●○○ Fluxspear - Does decent damage and stuns targets, and can also hit multiple targets. Stuns can be very useful, but you need to make sure you're using them.

●●●●○ Cross - Decent multi target spell, and also applies a debuff to enemies causing them to take more magic damage. The only problem I really have with it is knocking back enemies can be annoying. Most of the time you want enemies grouped together, not all spread out. Stuns do also negate knockback, however.

●○○○○ Nova - I'll be honest, I don't really understand this one. It broadly just seems like a worse Cross. It's a very small AoE that emits from your character, and only does about as much damage as a single tick of Fluxbolt. Sometimes, because the AoE lingers very briefly, you can get a double hit, but as far as my experience goes there's no way to achieve that consistently. Cross just seems like a far more useful option with a larger AoE, the ability to target groups far from you, and a debuff that increases your overall damage to the enemies it hits. This now has a 50/50 chance to stun enemies but I still don't think it's worth it.

●●●○○ Prism - Since the update this actually works much better. Now that it scales it's a decent skill to pick up, but bear in mind that it does take up a precious support skill slot. The 1 minute cooldown feels like a bit much compared to its actual power.

●●●●● Imbue - Buff skills are all mandatory picks imo. Unless you're in a coordinated group with multiple of the same class and have a dedicated "buffer" party member, bring your buff skill. It's just free extra stats.

●●●●● Restora - Also a mandatory pick, in my opinion. It's your heal skill, and it's really good.

●●●●● Blink - Very nice extra mobility, and it's a passive to boot. I highly recommend taking this. They even removed the MP cost!
●●●○○ Manaflow - I'll be honest, after the update, this really just doesn't give you enough MP regen to be worth a 6 point sink. And higher cooldowns also means you're spending less MP in general. Means Life Tap gets way more value though. Once you have enough points to pick it up as a leftover skill though, you SHOULD, because some MP economy is better than nothing.

So, a lot of stuff got kind of shifted around in terms of numbers and cooldowns and such, but it's mostly the same.

Classless skills are currently generally weaker options compared to class skills. However, there are a few skills definitely worth considering in your build:

Divine unfortunately was turned into a Paladin-only skill, so no more busted healing/aoe combo shenanigans for Mystic.

●●●●○ Life Tap - Woof. Update nerfed the cooldown of this from 20 seconds to 80. Despite that, it's still worth taking, especially with the nerf to Manaflow. Your mana consumption has also ramped way down with the update because of the cooldown increases, so it roughly lines up with when you need it most of the time.

●●●○○ Siphon Leech - Very good recovery skill. Possible alternative to Divine if you haven't gotten it yet, or possible to slot that somewhere else in a build for added tankiness.

●○○○○ Alacrity - Was originally decentish, but now with a tripled cooldown and general increases to cooldowns making it have less value to begin with, I don't think it's worth it anymore.

The update did see the previously not very good elemental spells tweaked somewhat, and some are even kind of competitive with spells like Fluxbolt now (we even got 2 new ones!):

●○○○○ Spire - Despite talking ♥♥♥♥ about some of the other classless spells, this one is actually okay. In theory it does pretty good AoE damage, with targets getting hit at least two times by the spires if not more (plus some bonus bleed damage if you're lucky), but the fact that it's a straight thin line really limits its potential, and targets seldom line up in a way that makes its damage output consistent. Man. This got hit with a nerf that it just did not need to begin with. 20s cooldown now. I just felt like I had to comment this because look at how they massacred my boy.

●●○○○ Talus - It's not bad, it's just not... good. I don't actually see any reason to take this besides doubling up on AoE skills. Does damage twice, but the first hit is a pretty small radius so you usually only hit one target. And the damage per hit is comparable to Cross. It also has a 50% chance to give a defense debuff (I hate this mechanic by the way, I don't like to gamble on whether the ability does stuff or not) but it's pretty miniscule. Cross just does more for you in terms of debuffing, and Talus's overall AoE damage potential is only slightly better.

●●○○○ Fira (previously Fireball) - Works pretty much the same as it did before. Does okay damage, but you have to get in close to actually maximize its damage potential.

●●○○○ Aquos - It's alright. Comparable damage to fluxbolt, though a little inaccurate. Could be good for splashing groups of enemies though.

●○○○○ Gust - I WANT to like this, but its cooldown is relatively long and the knockback is pretty severe. If you somehow have knockback immune enemies though (maybe combo from a stun?) you can get a max of TWELVE hits out of it which is insane. Normally though, this only hits like 1 or 2 times.

The main thing that really holds all of these skills back is their cooldown. Compared to the stuff you've got as Mystic, these would be a sidegrade if they had comparably short CDs but are just strictly worse in most cases because they don't.

We also got two new skills you can learn from Angela:

●●●○○ Crya (previously Cryo Needle) - Actually does more damage than Fluxbolt (for the record, the amount of needles is five, the tooltip doesn't tell you that. It's got a slow too, which is kind of nice.

●●○○○ Curis - Basically just an extra, slightly worse restora. Decent in theory if you really just want to stack a bunch of healing spells, but honestly kind of unneeded.

●●●●●Weapon Masteries are just great passives now and apply to all weapons of a stat type. And I could be wrong on this but I believe this means Mind Weapon Mastery would apply even to melee weapons if you change their type to Mind.

If anyone has any other weird classless skill combos I haven't thought of or tried, feel free to let me know.

In no particular order:

Actives:
Fluxbolt
Siphon Leech
Cross
Fluxspear
Restora
Imbue
Life Tap

Passives:
Blink
Mind Mastery

I use bells exclusively. Use imbue on cooldown. Cross's magic vulnerability debuff can be useful, even on bosses. Spam main attack (or charge attack, depending on bell) for multi target, fluxbolt on cooldown for single target and weapon as filler. Life Tap when mana empty, Restora to bump your health back up. Siphon Leech is also very useful for self sustain.