Building a leprechaun

[Quoz]

... Not really a leprechaun, but I want to make a full caster halfling who plays hell with the rules of probability.

The group I'm playing with has some particular quirks, and I want to make a character that works well within that structure.

- it's an informal group with a lot of first time players, and we rarely have the same players from one week to the next. Some weeks we are mostly Archers, the next it's all monks and clerics. The one thing nobody wants to play is pure arcane casters. We usually have 6-8 characters at any given session.

- each session is usually one big fight or a couple minor ones. I'm not sure we've ever taken a short rest.

- Our GM uses a much more aggressive crit and fumble format. As in, if you roll a natural one you just critically hit yourself.

We are currently level 3, closing in on 4. I doubt any character will last past 6 or 7. Rolled stats before modifiers 18 16 14 13 10 8.

I'm thinking a halfling (rerolling ones is a much bigger benefit at this table) and going either diviner wizard for portent or divine soul sorcerer. I'm not sure on a spell list but would like to focus on things that make the whole party better, so mostly buffs and debuffs. My first (And likely only) ASI will go to Bountiful Luck. I haven't played that style much in 5e so any input will be appreciated.

[Laserlight]

Perhaps take a level of cleric for Bless (and armor proficiency). Divination wizard's Portents is fun if your dice cooperate, although you get limited uses. Bardic inspiration would be another approach to manipulating luck.

[Mjolnirbear]

There is also Dark One's Own Luck from warlock, 'unlucky' spells like Hex and Bestow Curse, rerolls from Wild Sorcerer and, of course, the Luck feat.

I'd build a sorcerer-wizard. You only need Wizard 2 for Portent. Start class based on whether you want con saves or wis saves.

Then branch out. Search for the Luck domain cleric online. Or go Warlock for flavour.

[Rolero]

Bountiful Luck and Lucky should be obvious choices as your feats.

Instead of Diviner, I think that —thematically— a Wild Sorcerer could fit better as a randomness manipulator with the Bend Luck capacity they get at 6th level.

If you want to go all in, you could always dip into Diviner as well.

[Ventruenox]

I think that you are on the right track with the Divine Soul Sorcerer. With the Favored of the Gods ability, access to Bane, Bless, Guidance, and Minor Illusion, you can RP that character concept right out of the gate. Either a Charlatan or Urchin background would work well. Subtle and Quickened Metamagic are useful choices.

Ghostwise Halfling also gets you Telepathic communication to coordinate your party and can round out that one odd stat score. (18 CHA, 16(+2) DEX, 14 CON, 13(+1) WIS, 10 INT, 8 STR)

Given your table's critical fumble rules, the Bountiful Luck feat is an excellent choice. Citan had some of the best advice I've seen for spell choices in this thread.

[Particle_Man]

Wild mage sorcerer?

Or lots of prismatic spells for the pot of gold at the end of the rainbow effect.