Marowak is my fav Poke, so I'm excited for this form. I've used Marowak on my team forever, even if he's hard to use sometimes, but based off my current Marowak my thoughts would be this:
- With Thick Club, max Atk EV investment, he hits like a truck, I've never felt that something like Swords Dance or Belly Drum, would be necessary. If he hits; it hurts.
- Old Marowak, being a ground type physical attacker, basically had Lightningrod built in, but never found the electric switch-in super helpful or common. Then again Rock Head wasn't very useful then either, but now is, so maybe Lightningrod will be, but I'm leaning towards Rock Head.
- So I'd look at a set like:
Marowak-A @ Thick Club
Ability: Rock Head
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Flare Blitz
- Shadow Bone
- Bonemerang
- Iron Head / Flame Charge / Will-O-Wisp
Flare Blitz is your main attack, Shadow Bone for secondary STAB.
Bonemerang is their since it still hits pretty hard though STAB is lost, still breaks subs, and is still a signature move of Marowak's.
Last slot is pretty up in the air, Iron Head has treated me very well as a surprise move, knocking out everything from Azumaril to Xerneas on the switch. Flame charge is a nice new option to get some speed, if you know Flare Blitz would be over kill. Although you could run a more defensive set where Will-O-Wisp fits better, I think it still works to leave a lasting hindrance if you have no further use for Marowak-A in a match; though with the burn nerf, might not be worth it over other options.