EzioAuditore_1
One power I would suggest is Dimensional ruler. Dimensional Ruler: When staying in one dimension, he becomes able to sense and prevent other beings who are trying to enter that dimension. He can take over a world/dimension if it already doesn't have a ruler, alternatively killing the ruler lets him take over. He can also decrease the opponent's abilities with this skill should they step into a dimension under him and he can prevent them from leaving the dimension.After scathach's death he could take over the Land of shadows then revive scathach later and have joint ownership of the realm. There's no point in wasting such a good territory
I suggest arifureta and mahou sensei negima world for their magic which is conceptual in nature. If possible go the campione world and become a godslayer. After all it's only natural for a longinus weilder and a student of scathach to become a godslayer as well. If necessary go to fairy tail world and learn arc of embodiment and arc of time and other godslaying magic. His options are unlimited.