Sucker Punch is a viable alternative, but I would switch Pursuit instead because the Ai almost never switch. I would suggest you to bring a Water Type. Of course, Keldeo would be the absolute best with Suicune being also very strong, but I would say Starmie, Greninja or Delta Lilligant (Fire/Water) could be good partner for D.Typhlosion as Fire type check that also abuse the boosted Surf.
Fighting types will appretiate the Dark types you carry to cover Psychic and Ghost type and will help you cover opposing Dark type like Bisharp. Conkeldurr, Delta Scyther, Infernape, Lucario and Blaziken are all good ones.
You must also get a ground immunity. Since you aren’t using Levitate on Delta Volcarona, you will have trouble switching around them. Gliscor, Rotom and various other Pokémon are your best bet.
What set would you recommend for Keldeo, which of the fighting types seems to fit in the most, and which ground resist would I benefit from above all others? I’m sorry about blasting you with questions, I’m just excited to make this team and want it to not suck horribly.