Shooter HP: increase
Shooter DEF: increase
Shooter ATK: increase
Hartwell is a Healer and can be swapped out in Arena if other healers are banned.
Griffin and Hartwell find themselves in the awkward position of being two of the strongest shooters that provide bonuses to shooters. Unlike fighters for example, most five star Shooters provide bonuses to either troops generally, or bonuses to all three types: Fighters, Shooters, and Riders, rather than Shooters specifically making them terrible candidates for a Shooter troop formation, with some exceptions.
This then leaves you in the position of using five star hero Requiem whose skills benefit general troop formation because of lack of alternatives.
Unfortunately, either another blunder by the developers in design, or a choice, except unlike Riders which give you the benefit of speed, there is no benefit over Fighters in terms of stronger heroes. For this reason I believe this will be corrected eventually. Its possible that when designing heroes they did not anticipate the direction and benefit of formation to overall effectiveness and might.
At +5 Hartwell provides a +50% Shooter HP bonus, +50% Shooter DEF bonus, and +50% Shooter ATK bonus. She should be evolved to 210, and use in your Shooter Troop formation.
She can be obtained in Noah’s Tavern.