Unusual strategy possibility
 

While I'm sure it's rarely usable, it may be fun to attempt. If one has enough 'no retaliation' units (Royal Snake, Assassin, Imp, Vampire, Dryad, Fairy, did I miss any?). In a battle vs. army containing Devil Fish. Beat the fish down to just a few units 1-5 perhaps, using pet dragon smashing blow to kick the unit into the midst of your army while beating it down to a small stack. Don't attack the Dragon Fish, just let it attack you to get the critical bonus while fighting the rest of the enemy units.