Table of Contents
Video Showcase
General Strategy
To simplify things, we have color coded the teams to help players keep track of the arrows shown below.
Red Arrow = Team 1 bossing team
Blue Arrow = Team 2 Explosive
Yellow Arrow = Team 3 Piercing
Turn 1

Team 1 and Team 2: Move both teams towards the left tile towards the teleporter BUT DO NOT USE IT THIS TURN.
Team 3: Move team 3 towards the enemy above.
Turn 2

Team 3: Start turn 2 by moving team 3 towards the right on the activation tile.
Team 2: With team 2 using the teleporter they were on move to the upper left tile spawned by team 3.
Team 1: Followed by using the teleporter that team 1 is on then swapping positions with team 2 and finally moving towards the left side towards the activation tile.
Turn 3

Team 1: Move down towards the red teleporter that no team is currently on and use it. This should teleport you to the bottom left of the map.
Team 2: Use the teleporter that they are currently on and use it. This should bring you back to where team 1 started. Goto the new tile that has spawned below.
Team 3: Move right towards the last Heavy armored enemy.
Turn 4

Team 1: Move team 1 down to deactivate the tile that team 3 is currently on.
Team 3: Once team 1 has deactivated the tile, team 3 should now be at the starting point. Move to the teleporter below and use it to join up with team 1.
Team 2: Move towards the bottom left tile with an enemy.
Turn 5

Team 2: Move team 2 towards the activation tile to their left.
Team 3: Then move team 3 towards the tile below to the right of team 1.
Team 1: Finally swap positions with team 3 and move right to reach the boss.
Team Building

As for team building in challenge stage 4, you will need 3 teams. Two of these will consist of AoE Explosive damage dealers with some Single-Target mixed in for the bossing team. Team 3 will consist of AoE Piercing damage dealers to deal with the Heavy armored enemies. Then, bring tanks, healers, and general supports as you see fit.
Character Recommendation
Note that characters listed here are only some of the viable options
Piercing AoE
Explosive Single-Target
Explosive AoE
General Supports
Healers
Tanks