Would you like to see elephants with bombard cannons on their back? Unit has the same stats of hp and armour as the elephant archer, but has 12 range and the damage of a bombard cannon.
Basically the unit is a high hp bombard cannon unit. That can be healed by monks since it’s a cavalry unit.
They could be an untrainable unit, that can only be trained in scenarios, to stop guys whining over how overpowered they are. You need to add a trigger to allow training of Bombard Elephant. Or spawn them with create unit in order to have them in game.
This unit exists in AOE 3. https://ageofempires.fandom.com/wiki/Siege_Elephant
And in Medieval 2 Total War: https://www.youtube.com/watch?v=Myhj-nEywyg