This enemy shoots a harmless bullet in a high arch which pierces characters, and explodes into 9 fire clouds when it hits the terrain, like the Gunner's M9 Grenade 6. This enemy can be fairly dangerous, as it has an incredible range, and the flames left by the bullet are close together and can rapidly deal damage. Having a melee character get into attack range and using the dodge strategy is the best way to take them out, preferably with a status-inducing weapon.
Another strategy to defeat them is to take advantage of the bullet doing no damage via the bait strategy. Placing a character high in the air slightly in front of the other party members cause the Walker to aim towards that character, but will be unable to deal damage as a result of the bullet itself dealing none. The bullets will also fly over the other characters' heads, as a result of the high arc they fly in towards the bait. Care must be taken to ensure the bait remains in the optimal position to both direct the walker's attacks, and ensure the attacks will not strike the other characters. Just be mindful of the White Triangle Stickmen and the occasional Orange Triangle Stickman.