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In Sword/Shield you no longer need HMs to do certain things (e.g. fly and surf) so instead of needing the move dive in future games you could get scuba gear as a key item and that could let you dive. You would be able to customise your diving gear. For under the gear there would be a few swimsuits and wetsuits. For gear you could choose between LAMA gear, modern scuba gear, vintage scuba gear and some kind of simplistic slightly futuristic full-face oxygen mask.
(I would really like there to be some kind of oxygen mechanic meaning your character would black out after running out of air but that's too morbid for a kid's game also this is the longest 4chan post I have ever made)
