i beat COT5 by useing goblin, bomber, dwarf, centuar, mermaid, and witch for units and for specials, i used pheonix strike, comet shoot, crystal thunder, chrystal freeze, Athena protection, and arrow. ( try to have them maxed out ) the stuns and long range units will keep pushing it behind the enemy castle. but if the goblin does make it passed your defenses, keep trying. thats what i did