Your rental Pokémon will probably take a beating the new Dynamax Adventures in Pokémon Sword and Shield’s Crown Tundra expansion pack. These Dynamax Adventures have you and a team of three other trainers diving into a Dynamax nest where you can potentially capture a new legendary Pokémon. Numerous other Dynamax Pokémon are blocking your path, and defeating them brings you closer to your real prize. Because it’s a dungeon-like task, healing your Pokémon is a top priority, but you won’t have access to your inventory.
Instead, you have to switch out the Pokémon you’re using for a new one. You can only do this at specific times. The only to switch out your rental Pokémon is to trade it for the Pokémon you just defeated or to encounter an NPC who is in the Dynamax Adventure pathway, speak to them, and trade it for your current rental. You can only do this for one of your party members.
If two party members have weak Pokémon, you’ll have to decide between the two of you who receives the new one. You’ll have to plan your strategy of how you want to adventure deeper into the adventure, so make sure to communicate with your teammates.
You can take a quick preview of the path before you accept it, so this might give you a good idea of where you need to go. However, you can only keep one Pokémon you’ve captured once you exit the Dynamax Adventure, and chances are it’ll be the legendary Pokémon waiting at the end.