The Merge Heroes process is confusing me. I got both the one star and two star Hana's from the event. Which should I sacrifice when merging?
Don't know if that's always the case, but for me both Hanas had the same stats, so it depends on what you want to invest:
In my case, I already got the 1* when the map first came around, and kept and leveled it. Now the second time, I managed to score the 2* as well, and was stumped on what to do.
In the end, I leveled the 1* a bit more (was already Level 17) to bring it to 2* - and it turned out that on 2* rarity, both had the exact same stats.
So I took the one I had already leveled, because she already had abilities and some leftover SP, and fused the newly gotten 2* into her.
I gained a 2* Hana with an extra level, and 20 Skillpoints extra. I think that was a good call.
Alternatively, you can send the 1* home for a ridiculously low amount of feathers (15 I think?). Upgrading to 2* is really cheap in comparison. If you intend to use Hana, I'd suggest leveling the 1*, upgrade it to 2*, and fuse the spare 2* into her.
The other way around you will only get 10 SP by fusing the 1* into a 2*.
Generally, always sacrifice the lower into the higher, or of equal rarity.
You gain a bonus level when merging a higher rarity into a lower rarity (or equal) - however an extra level is nothing compared to higher rarity - and you lose the extra level when upgrading to higher rarity eventually (the upgrading will cost a bit less though to make up for it).
For slightly higher rarities (2* or 3*) it might be worth it to send the units home to gain some extra feathers instead of merging, since Skill Points can always be farmed as well, but you might need a few feathers urgently for some upgrades.