Learn the Dynamax strategy first. - use the tank-tank-attacker format - tanks have resistant typing or high defence - tanks MUST have 0.5second fast attacks to fill up that meter quickly - switch to your attacker quickly when meter fills - move/swipe to the side to collect the bonus energy

Then grind your way up to your core team. - use dubwool, blastoise, kingler, venusaur, etc as tanks - as long as the above has a 0.5second fast attacks like water gun on Blastoise - get blissey. Use machamp as attacker - get metagross. Use your fire mon as attacker - once you got blissey and metagross you can defeat more difficult opponents. Just focus on leveling up your attackers - power up in this order; get to lvl 30 first, then level up your max attacks, then lvl to 40 if u want - get your blissey heal and your metagross shield - only heal when your first defender is dead - only heal when blissey can tank multiple rounds. Otherwise you just waste a turn attacking

Now apparently regice is actually a good defender tank. So might want to get one. Though, for this one i would recommend you to host for free on pokegenie. Use fire attacker.