I had the easiest time with him, just try and keep a flexible team (at least until legendaries/pseudo legendaries) and catch a variety. The only ones that stayed in my team for long before that were lucky hidden grotto finds and shinies.

EDIT: Oh and get Ayylamos with the natures you like using, it makes the nature grind so much fucking quicker. I just did Sp Att for Att and Att for Sp Att, but you might prefer speed/tankiness I just prefer grinding speed EVs then sweeping the tough fights with a team of hard counters. Also near the ghost tower grab a sprucifix with wonder guard asap because it's OP as fuck when it works.