In my search of a +def/-HP Fae, I often pulled green in banners in which green focuses were good.
Sadly I haven't found one since launch, but the banners in which M!Grima were a focus were a blessing. I got 5 of them as F2P, that's amazing since I usually get non-focus units in all other banners.
So the question is, as a F2P it's better to just use those grimas as fodder to strenghten my armor and dragon core, or it's better to try my luck and use orbs mostly on banners in which he's a focus to get a +10 Grima for arena? He's premium fodder but my arena core has low BST even with high merges.
Reinhardt is a pistol in a knife fight.
Blyn is a rocket launcher in a gun fight.
Male grima is a satellite orbiting earth dropping solid tungsten rods from outer space to cause nuclear bomb levels of destruction.
Seriously, male grima has built in dc, can run steady or warding brath, bold fighter, and quick riposte, so that no matter what hes doing, he's going to give someone whose unprepared a very bad time.
I wouldn't bet on your chances of getting a +10 Grima as F2P anytime soon. With that said, whether or not to fodder him is another question. It really depends on what your arena core is and what your goals are with dragons.
To be honest, the dragons are flexible enough to not necessarily need dragon buffs in their C slot. For example, I run Fae with Atk Ploy/Res Ploy in C/S slots and Tiki with Atk Smoke in her C slot.
Pokemon GO
Fire Emblem Heroes
Fate Grand Order
Dragonball Legends
Dragalia Lost
IV Calc
Heroes