new chain challenge for those story maps is actually pretty difficult. The two that come to mind being the limited turn one on map 5 and also Myrrh's map. Can't say anything about the former except do your best, but I do have a suggestion for the latter map. The Myrrh map is really difficult because the enemies are stationary and so you have to bait them for them to start moving. They're on the other side of a wall splitting the map in half, which makes it difficult to get in while also being able to get out. Lv40+ stats means you likely won't be killing them in one round either. Further compounding the issue is the coverage they have on the tiles you have to bait them on if you choose to do so: both in terms in colors and in terms of physical/magic damage. Also the two dragons in the middle are honed/fortified respectively making it even more difficult.
My solution was to send Elise in to hit one of the dragons in the middle with a gravity, then have the bait unit reposition her back. Since the gravity will hold the middle two dragons in place for a turn, you're free to leave your bait units in range for the two outer units to kill themselves on. Once you've done that you should only have the dragons left to deal with and they're separated, making them much easier to deal with.
Gravity, as I've come to appreciate, is really really useful sometimes.