Oh, I see. You meant the legendary tier of the Event quests
So as far as season 2 goes, color stacking helps a lot in the last 10 or so provinces of Normal difficulty, and in all stages of Hard difficulty. I personally color stack against the minions, the boss if I can. If I can’t then I try to make my stack deal at least neutral damage or bring some items to help me (bombs, banners, potions).
Stage 19.4 is poison mist, green minions and Chochin boss. For that one I’d bring Kiril, Gormek, Sumitomo, Li Xiu, Hansel. Boldtusk would be better than Kiril but he’s too far down in levels. Ditto Wilbur, he’d be better than Gormek but again he’s too far down in levels.
Get Mitsuko to 2.60 and park her there. She won’t hit hard but she’ll still be useful against the Kirin bosses that are coming up (they basically suicide into her blue reflect), and she’ll be bulky enough for Normal difficulty minions.
As for the heroes to focus on, I’d recommend 4*s to ascend before 5*s. As I said, color stacking helps a lot in these final stages, so having strong options in all colors quicker will be more helpful to completing the campaign.
Wilbur and Proteus are awesome, I’d max them first easily. Even with Hel, it’s really helpful to have Proteus anyways, pair both together and bosses in any stage will never fire their special skills. Merlin is great too, and so is Boldtusk. Those two should follow being maxed immediately afterwards.
Hu Tao and Chao are mediocre unless they’re emblemed, since their class trees can help fix their shortcomings. Danzaburo’s special skill is risky, but 2/3 effects are very powerful, personally I think his reward is worth it, and a good addition to a yellow stack.
Triton is far better than Agwe and worth maxing before a duplicate Kiril imo, he’s an offensive sniper with a great support buff.
Melendor should be your next green choice, he’s Sabina’s green counterpart basically.