Here are my results about Royal/Dark hybrid ( Opponent Impurrious):
(Use against Royal/Dark hybrid) Strong: Birthstone; Fairy; Fire; Halloween;Magic; Realm Rune; Royal ; Service; Space ( Planet); Treasure; Tree
(Avoid using against Royal/Dark hybrid) Weak: Christmas; Dark; Legendary (crystal); Lucky (Shamrock); Valentines; Winter
Neutrals with Royal/Dark hybrid: Autumn; Earth; Egypt; Electric (lightning); Ice-cream; Music; Nature; Rainbow; Spooky; Spring; Water; Zodiac
Currently untested with: Bomb; Food; Skull
(All tests are done on IOS device, based only on Strong/ weak / neutral hits. Critical hits have not been taken into account. )