The official Pokémon website has announced the full details for the Pokémon Sword and Pokémon Shield Ranked Battles April 2021 (Season 17).

Pokémon Sword and Pokémon Shield Ranked Battles April 2021 (Season 17)

Spring into action with one usually restricted Legendary Pokémon on your team throughout the month.
A new Ranked Battles season is here, and with it comes fresh opportunities to test your battling skills. The leaderboards reset every month, so now's the perfect time to jump in. The Ranked Battles April 2021 Season (Season 17) will follow the Series 8 regulations, which means you can battle with one powerful, usually ineligible Legendary Pokémon at your side.

Battle head-to-head against players around the world, move up the global leaderboards, and earn helpful in-game rewards throughout the month!

Only Pokémon obtained in Pokémon Sword or Pokémon Shield or those with the battle-ready symbol are eligible. Pokémon from previous games in the Pokémon series can receive the battle-ready symbol from the character next to the door in the center of the Battle Tower. When the battle-ready symbol is applied to your Pokémon, your Pokémon will forget the moves it knows. If your Pokémon forgets moves that it cannot use or learn in Pokémon Sword and Pokémon Shield, those moves cannot be relearned.

Eligible Special Pokémon

Only one of the following special Pokémon may be registered to your Battle Team: Mewtwo, Lugia, Ho-Oh, Kyogre, Groudon, Rayquaza, Dialga, Palkia, Giratina, Reshiram, Zekrom, Kyurem, Xerneas, Yveltal, Zygarde, Cosmog, Cosmoem, Solgaleo, Lunala, Necrozma, Zacian, Zamazenta, Eternatus, or Calyrex.

Ineligible Pokémon

These Pokémon are not permitted on your Battle Team: Mew, Celebi, Jirachi, Victini, Keldeo, Genesect, Diancie, Volcanion, Magearna, Marshadow, Zeraora, Meltan, Melmetal, and Zarude.

How to Start a Ranked Battle

To start a Ranked Battle, follow these steps:

1. Launch your Pokémon Sword or Pokémon Shield game.
2. Open the X menu.
3. Select VS.
4. Select Battle Stadium.
5. Select Ranked Battles.

April Season Rewards

Before battle, you'll be matched up with other players of similar rank to ensure even competition. The higher the tier you finish in, the greater the in-game rewards you'll receive after the season concludes. The April 2021 season rewards include the following.

Master Ball Tier

• Gold Bottle Cap ×3
• 600 Battle Points
• Dynite Ore ×30
• Armorite Ore ×30

Ultra Ball Tier

• Gold Bottle Cap ×1
• 300 Battle Points
• Dynite Ore ×10
• Armorite Ore ×10

Great Ball Tier

• Bottle Cap ×3
• Ability Capsule ×1
• 100 Battle Points
• Dynite Ore ×5
• Armorite Ore ×5

Poké Ball Tier and Beginner Tier

• Ability Capsule ×1
• 50 Battle Points
• Dynite Ore ×5
• Armorite Ore ×5

How to Receive In-Game Rewards

Once the season is over, you can collect your in-game rewards. Remember, you will need to finish at least one match with a win or loss during the April season to be eligible for rewards at the end of the season. To receive your in-game rewards, follow these steps:

1. After the competition has ended, launch your Pokémon Sword or Pokémon Shield game.
2. Open the X menu.
3. Select Mystery Gift.
4. Select Get a Mystery Gift.
5. Select Get Battle Stadium Rewards.

Good luck battling in the Ranked Battles April 2021 Season!

Source: https://www.pokemon.com/us/pokemon-news/pokemon-sword-and-pokemon-shield-ranked-battles-april-2021-season-17/