Fire Emblem Fates: Birthright
I've been stuck on one mission for MONTHS now, because I couldn't find the time to really buckle down and grind through it. The Nohrian army was just too big, their formations too complementary for me to crack without losses. But I finally did it. I got through the first phase, and the pair of super-strong retainers at the gate. Then I realized there was a second phase with a lot more really strong dudes and a boss at the end.
But there was some environmental hazard stuff I could do to soften 'em up, and it worked great! My dudes are cutting though the berserkers and knights like butter. I moved Silas to bait out literally one of the last enemies, a berserker. I did the math, Silas was 100% safe from death, and he'd get a good bit of exp from the fight. So this berserker just saunters up, and on a 3% chance, criticals Silas. He down, he's out of this fight and all the others; for story reasons, he's "retreated" but he's basically dead.
So now, do I restart the whole mission, again, to save Silas? Usually, yes. But I never really liked that guy anyway.