I had way more Nino's then I needed so I said "Hell, why not try a +10 Nino"
Right now I am at 40+5, but I am having mixed feelings to continuing it, then again I don't have any other high unit merges....
Stopping at +6 is an option. You get an extra point of spd on the 6th merge.
I generally don't recommend merging Nino because I think of her as a buff-dependent unit, i.e. she's extremely strong with buffs, much more so than other units with equal merges and buffs, whereas some other units can use all 4 or 5 stats better.
I would say it depends...
-Do you really like her, or did you merge her just because you happened to have several copies?
-Are you an arena player? If so, what tier do you normally reach? What tier would you want to reach?
-Is there anyone else you're certain you'd rather merge down the line?
In that case, I'd rather use units that you like and merge them up. Soleil is an excellent choice, she scores pretty well and has a great stat distribution.
Nino is a solid mage but honestly, she's a bit dated. She's great at killing things but there are mages that can perform her role and provide some utility to the team, like Soren and Lilina.
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