Back in Pokemon Sun & Moon, Totem Lurantis was one of the more difficult Pokemon to defeat. And in Pokemon Ultra Sun & Ultra Moon, this continues to be the case. On top of having its speed increased by one stage as the battle begins, Totem Lurantis will also call upon Pokemon that will use the move Sunny Day. With this move, Totem Lurantis will then be able to instantly charge is Solar Blade within one turn, as well as fully heal itself by using Synthesis. Before you know it, you could literally be swept by this Pokemon, making the Typing of you Pokemon all the more crucial.
If you would like to avoid having difficulty with Totem Lurantis, definitely consider trading for the Arbok in the Route 8 Pokemon Center. Arbok can take every move Totem Lurantis as to deal, while still having Poison Type Attacks to send Lurantis packing. The trades for Hawlcuha back in the Route 2 Pokemon Center and for Noibat in the Route 5 Pokemon Center can also come in handy here. If you have a Pokemon that knows the move Taunt, it could also help prevent Lurantis' allies from using the move Sunny Day, crippling the Totem Pokemon before it can get going. Having the Fire Starter Pokemon of the region will also pay off with this battle.