Borderlands 2 style:
Piercing = Corrosive (effective on robotic/armored enemies) or Shock (effective against shields) or Slag (makes enemy more vulnerable to another damage type)
Explosive = Fire (effective against flesh, or permahealth = permahull)
Impact = Explosive (jack of all trades)
Also this
Mine = NPC Paladin AOE Spell.
You get a salute and a cookie