Finally beat all the caves... The fifth one was nearly lost, because the goblin had launched over my main squad and was RIGHT NEXT TO MY BASE when the main force destroyed the enemy castle... PHEW!
Beat first 3 caves, 4 is pretty unfair (Come on, 2 lava titans and a shadow titan?) and 5... I'll be working on a strategy for that. I've noticed that the invisible goblin can be knocked back, so I'll work out a plan.