The way to beat Cave 5 is to use stuff that immobilizes the shadow goblin for a little bit
: the fireball spell, succubi, and mermaids work very well. The exact setup I used was succubus, mermaid, armor, dwarf, centaur, cannon, fireball, comet shoot, freeze trap, lightning bolt, athena protection, hercules' strength...beat him second try.
 "Journalière")
 "Epic War 3")