Build Help for a Level 12 Dungeon Crawl

[Legato Endless]

Just got invited to a new Friday game, mostly combat, very little rp.

DM wants a level 12 character build beforehand. Party currently includes: a fighter, ranger, wizard and an artificer. Haven't gotten any real details about their builds beyond the classes.

Standard array for stats, normal starting equipment, 3 uncommon magic items and 1 rare magic item. Supposed to optimize for a lot of fights. No Unearthed Arcana. Haven't done much 5e beyond levels 1-8, would appreciate any build help. Especially not sure what do with magic items, my last two campaigns the DM banned their usage.

Concept wise, I'm pretty open, was thinking something heavy hitting for melee, but I'm not picky.

Thank you for any insight.

[CheddarChampion]

Perhaps a Rogue specializing in traps?
Expertise in Stealth, Thieves' Tools, Perception, and Investigation.
Ask your DM how often you might get Crits if you go Assassin.

Wood Elf 10/17/14/10/14/10, pick up Elven Accuracy (+1 Dex), +2 Dex, Alert, Dungeon Delver.
Otherwise High Elf Arcane Trickster 8/17/15/14/10/10. Elven Accuracy (+1 Dex), +2 Dex, Resilient (+1 Con), Dungeon Delver.

[J-H]

Druid offers healing (lacking in the current party), crowd control, and possibly melee.
Cleric may be an option, or the celestial heritage sorcerer, if you want a couple of other healer-approaches.
Or bard.