The Mage has the smallest hit die, a d6, and the longest reach. The ready-made hero starts with 18 Intelligence and casts Fire Bolt, which deals 2d6 damage and reaches enemies melee cannot.
Play a MageSave Fire Bolt for enemies who stand far away, since your allies cannot reach them.
Each cast uses a spell slot, and a long rest restores them.
Stay out of the front line. Few hit points go quickly.
The Scholar background adds Intelligence and training in Arcana.
The Tough feat helps cover your low hit points.
You can still attack normally, and a long rest brings every slot back.