Competitive deck idea (Want feedback)

You're playing too many cards that Just don't help your deck play. Accompanying Flute, Kieran, Handheld Fan, Hassel— to name a few. You want to replace these cards with consistency staples like more rare candy, iono, Night stretcher, Earthen vessel, buddy puffin, nest ball, Fezandipiti and radiant greninja. Also you shouldn't play cards like Swirlix and Enamorus that have useless attacks. Replace them with cards that can assist your deck.

Once you've dealt with that problem, you're going to instantly start doing a lot better. Even though the deck is still not incredibly good— that being due to Dipplin just not being a good pokemon— you can make it decently good. It still won't be able to compete with decks like charizard and Miraidon, but it never will, so if you just really want to play this build then this is the best advice I have for you.