There's no reason to use a switch. The high level overview is that you want a location to always follow your hero unit. When an enemy enters this location, you move the units to the battling area (and leave the trailing location where it is). When the battle is over, return the hero to the trailing location.
| Trigger |
| Description: |
| Trail the unit |
|
| Conditions: |
| ¤ Current player brings exactly 0 any unit to battle area |
| Actions: |
¤ Center location labeled "Trail" on hero owned by current player
|
| ¤ Preserve trigger |
| Trigger |
| Description: |
| Start a fight |
|
| Conditions: |
¤ Current player brings exactly 1 hero to "trail"
|
| ¤ Enemy brings at least 1 any unit to "trail" |
| Actions: |
¤ Move all hero owned by current player at "trail" to "battle area"
|
¤ Move all any unit owned by enemy at "trail" to "battle area"
|
| ¤ Preserve trigger |
| Trigger |
| Description: |
| Fight's over |
|
| Conditions: |
¤ Current player brings exactly 1 hero to "battle area"
|
| ¤ Whatever conditions for victory |
| Actions: |
¤ Move all hero owned by current player at "battle area" to "trail"
|
| ¤ Preserve trigger |
Assuming that you don't want the units to fight in the "overworld," you should make all the units invincible when they are not in the battle arena, and then make them vulnerable when they are moved to the arena.