well i've done it once already but its really demanding on higher difficulties since sometimes you wont get to choose who you pair up with. i think i did it by marrying off every single wife candidates of Chrom and having Olivia and Chrom pair up on that chapter. also how can i even dance 20 times on that chapter? Gangrel moves on Turn 5 or something near that and every single enemy on the map is aggroed against you so you cant stall for time either. i think Rightful King would be great with Lethality but since no child bar Morgan can have that skillset its not really viable. ugh if only Lissa and Chrom weren't siblings and could marry >.<
Hahaha not gunna lie, I don't use Lissa. :P I don't like her character. I play on normal and hard but when I tried Lunatic, I get a**f***ed. I lure out Gangrel and I use the rest of my troops to run away. I try to use fewer units during that chapter so that the aggro enemies take longer to reach. At the beginning, I won't move my characters so I have a few more turns to dance.