We choose Luna as the starting hero at the Conflux.
For the second hero, we build anyone with a ballista.
...and then there are two options:
1) We take 2x1 upgraded sprites + a ballista, gain +1 level (basic artillery and +1 to attack), and attack... depending on the battlefield, the task is to create a wall of fire so that all non-upgraded units die immediately - or you can use 2 walls... with one sprite, we retreat, and with the other, we distract the upgraded stack so that it switches to attacking the ballista on the 2nd or 3rd turn - but the ballista shoots it down in a couple of rounds.
2) Luna attacks the non-upgraded stacks, and then the garrison with advanced artillery and 5 attack points attacks the upgraded stack.