Current questions and answers regarding the map editor.

How else can I trigger a battle?

1st way: using 'StartCombatom' (as already suggested)
2nd way: You can also do it differently - make the script run regardless of whether the player is the attacker or the defender. No triggers are needed here; it's done by adding a few lines of script to the 'combat-common.lua' file - this file is launched by the game when any battle starts.
PS: The second method is more versatile for various battle situations. You can also add a check for specific heroes.