Board Thread:Questions and Answers/@comment-151.224.83.90-20150701233428/@comment-26297531-20150702004547

darvanshel, shera, and elimo are good mitigators to have. elimo has 7 stars evolution, and is currently 1 of the best mitigator unit that can heal and null statuses too. As a new player you probably do not need mitigating, but they are a must in higher raids and trials. Also, training up at least 2 mitigators is a good idea, for some trials/grand quests require multiple mitigators in different squads.

next, tridon, hadaron and dion are good sub-units to have. dion is a better kira, and crit buffers offer the most damage increase, followed by spark, then attack, then ignore def buffs. these 3 are also 7* units (tridon and hadaron's coming soon). tridon is extremely useful to have, and as a lead provides some bit of additional mitigating.

as for your others, elaina is a passable 7* healer, carrol is quite a global exclusive unit to have. Ok lead for BB spam, and multi element buffs are useful in raids and frontier hunter. melchio is a unit to keep too, because in japan version they have his 7* form released. your other units are pretty meh... rina is good for her paralysis debuffs until you get better status inflictors.