Board Thread:Event Help/@comment-5200244-20170807170750/@comment-31063493-20170809231524

In order of importance:

Chilled (he's your main damage dealer)

King Vegeta

Mecha-Frieza

Tao The others don't matter as much since the utility that they provide isn't from damage.

As Gilaad said you could get them all to 15 but it is possible with only Chilled.