How to beat Gigantamax Mackogneur
Before going any further, Gigantamax Mackogneur is exclusive to Pokemon Sword. This means that you won't find it at all in a Raid Max in Pokemon Sword, even after downloading the Wild News or connecting to the internet in the game. You can however exchange it for Pokemon Sword from Shield, so you can have it if you really want to get it.
Unlike some of the more difficult Max raids you'll come across in Pokemon Sword and Shield, Gigantamax Mackogneur luckily only has one type that you will need to worry about offensively, as this is a straightforward type of combat. This means you're going to want to tackle it with flying, psychic, or fairy attacks that go right to its weakness.
Gigantamax Mackogneur has a few moves like Max Flare at its disposal that can deal good damage to most types, but one attack you can really prepare is the earthquake it has. Bringing in a Pokémon with Flying as at least one of its types, such as Corvaillus or Togekiss, can be of great help, as it can completely avoid taking earthquake damage. Togekiss in particular is a good Pokemon to use here, as it has the dual Flying / Fairy typing, both of which are strong against Gigantamax Mackogneur.
While you might think Gigantamax Mackogneur would have a solid defense, it really goes pretty easily for a five-star raid as long as you usually have another live player to help you out. This can usually be accomplished by pairing up rather than needing a friend to help you out, but you can handle it however you want.
Once you have defeated Gigantamax Mackogneur, you will have the opportunity to catch it. Your best bet to catch it will be in an Ultra Ball, but that's far from a guarantee that you will actually catch it on the try that you get here. If not, you will have to find another Max Raid with Gigantamax Mackogneur and try again.
