Karsticles
Member
The best way to resolve the issue of solo characters is to give solo assists. Every character had an assist that becomes available only when he or she is alone. Example: Viewtiful Joe calls Silvia in, Amaterasu calls in Issun, etc. This would be easy to balance, and it would ensure everyone has a comeback option. I can't think of any Capcom characters that don't have friends to summon, and it would help spread representation.X-Factor is good though.
Dante + Lady
Ryu + Ken
VJ + Silvia
Ammy + Issun
Rathalos + Rathian
Morrigan + Lilith
Felicia + Cat Helper
Etc.
The solo assist would be pre-set and not changeable.