I have not used elephants much, but my brother found Armoured Elephants work well against enemies like Dacia, they can break in the wooden gates, and demolish the light infantry. Be wary of their archers, though, if you try that, though he did not have too much problems with that; probably they tried to avoid friendly fire. I have had the enemy archers open up on my elephants with flaming arrows. The only other times I have seen the enemy use flaming arrows have been against siege equipment and onagers. Elephants are awesome against chariots, found that out from curiosity. Only problem is, Egypt has the archers to counter the elephants. Against legionary types of infantry, had a friend in custom battle put his Armoured Elephants against Urban Cohort. He lost. The pila demolished his elephants and Urban Cohort are good enough to finish off the rest. If you watch, when elephants are trying to ram the gate of a stone wall (of any size), the boiling oil kills the people in the basket before it kills the elephant, so it takes several bouts of oil to kill the beasts themselves. They will usually run amok before they get to the last elephant.