So my lvl 3 Paladin just crit with a Maul for 58 damage. Here is what I did.
Great Weapon Fighter
2d6 Maul
2d6 Had just cast Thundering Smite
2d8 After hitting used a spell slot to Divine Smite
+3 Str
So after the crit I rolled 8d6+4d8+3 (and rerolled 1-2's for Great Weapon Fighter)
Did I do...
