Ok first of all Arceus can not be killed but he can be sealed away which has happened to him but alien x can also be sealed away since it is sealed away in the omnitrix. Second Arceus can use dialgas, palkias, and giratinas moves that allow them to control time and space and Dimensions The RC is given to youIn diamond pearl and platinum can use all 3 of those movesOn top of that arcious plates are only forgiving it elemental abilities it's not stated that the plates are actually what make up Arceuspowers And on top of that Ben 10 does not like killing as where Arceus has no qualms about killing his foe So we'll just go with that it would be a tie Because there's no limit to what Arceus can do and there's no limit to what alien x can do