Assassin

Assassin is the mobility class. Guides send it behind the enemy line to cut archers and commanders. A creator test mentions a mount making those flanks easier. Another comparison calls it the fastest and highest personal damage of the original three, with the lowest health. It does not require cavalry troops.

Chosen in the tutorial, or a reported 50 Gem switch.

Play away from your own shield wall. If you stay behind your troops, you paid for a class you are not using. It is the right cover for a map with several entrances.