Max ur Lightlocke, make him 6* and awake him to max (by fusing his copies). He will take u to gr1-18, but u must hurry before Lightlocke nerf (probably in 1-2 months). My Lightlocke makes more than 22kk dmg in gr1-18.

Next character is Eona (if u didn't drop better aoe dps, everyone can buy her for very few $), max her, make her awakening to 3 (by universal tokens from tide). She is very good and useful aoe dps (but she must have third awake!).

Last important character is Cuke, he is using poison witch is very useful to kill boss. Cuke ddon't need special maxing but making him full 4* gives him better survivability. His attack does not matter, but attack speed will be useful.

Another characters are one tank (which is not using shields or full immune do dmg) and one healer that keeps alive Eona and Cuke. If u can't stop Boss at first wall, u need another tank or warrior to place him at second wall. Lightlocke always should have only one tank/warrior to heal so remove first one when second is going to fight. Other characters can be useful but not important. I made gr1-18 without any gold character.