Marshal is the fourth member of the Unova Elite Four. He is located in the east room of the Pokemon League. His Pokemon are all Fighting-type, with two dual-types. All of his Pokemon still have weakness to Psychic-type attacks, so you can breeze through with a Psychic-type. Marshal says he is grateful to challenge you again and wants to improve his bond with his Pokemon through another fight with the Champion, which is you. A quick flash of lights, and the battle begins.
His first Pokemon is Breloom, a Grass/Fighting-type Pokemon. You can immediately see that it has a 4x weakness to Flying-type moves. Be careful not to risk physical moves; since its Ability is Effect Spore, it could give your Pokemon a random status problem with contact. It uses Sky Uppercut and Spore as a combo move. It is a very good idea to use a Full Heal, because it will immediately resort to attacking the next turn; plus, Spore is 100% accurate.
Once you’ve beaten it, another Pokemon that could be sent out is Mienshao. Its opening move is almost always Fake Out, unless you have a Pokemon out that is weak to Fighting-types. To get the most out of your turn, try healing your Pokemon, because Fake Out always causes flinching.
Next is Sawk, a slow, but sturdy Fighting-type. It has the uncanny Ability Sturdy, preventing it from one-hit KOs. This means that even if Marshal uses a Full Restore, Sawk cannot be KO’d at full health. Try a weak move first to void the Sturdy, then use a powerful move and blow it out of the water.
Marshal’s fourth Pokemon is Throh, which is Sawk’s counterpart. Fortunately, it has Guts, which boosts Attack when it has a status problem. If you have a powerful Psychic-type move, don’t be afraid to use it. I forgot to mention that Marshal’s Pokemon are a bit slow and a Pokemon with decent speed can outrun them.
Watch out for Marshal’s next Pokemon, which is Conkeldurr. It has very good defensive capabilities, and a lot of HP, since the bar moves very slowly. It uses Hammer Arm, which is a very powerful Fighting-type move. It lowers its speed, but Conkeldurr is slow enough, so it doesn’t really matter. It may take a few hits to defeat it, so use a Pokemon resistant to Fighting-type moves, or use a Ghost-type. This is by far Marshal’s toughest Pokemon, but usually it’s his last, so be glad it’s over once you’ve toppled this giant.
Finally, the last Pokemon you’ll see is Toxicroak, the Poison/Fighting dualtype from Sinnoh. Fortunately, it has a double weakness to Psychic, and has no moves that would be supereffective against them. I would say that a medium defense is okay, since you can probably take it out in one hit with just about any Psychic-type move. When you win, Marshal will say that no one Pokemon team can win every battle, but improving your team to cover for its weaknesses is something he respects you for. You can then move on to fight the Champion if he is the last of the Elite Four.