The Water & Wind event will run from August 15th to August 27th (time zones applying). For this event, you can only use WATER and WIND monsters. You can earn medals by playing Duels and you can obtain the following rewards according to the number of medals you have:
50 to 11000 medal threshold: a total of 1900 gems
12000 to 21000 medal threshold: a total of 20 Legacy Pack tickets
Additionally, at the following thresholds, you can get these rewards:

The following Forbidden/Limited List changes will be applying for the event:
Forbidden:
All non-WATER and non-WIND monsters

Barrier Statue of the Torrent
Kashtira Unicorn
Mist Valley Apex Avian
Moulinglacia the Elemental Lord
Wandering Gryphon Rider

Baronne de Fleur

Apollousa, Bow of the Goddess

Cauldron of the Old Man
Chain Strike
Clockwork Night
Cybernetic Fusion Support
Dark Snake Syndrome
Deck Lockdown
Dimension Fissure
Double-Edged Sword
Final Countdown
Fire Prison
Floownadereeze and the Advent of Adventure
Galaxy Wave
Hippo Carnival
Jackpot 7
Lair of Darkness
Level Limit – Area B
Life Hack
Messenger of Peace
Mikanko Water Arabesque
Misfortune
Moon Mirror Shield
Necrovalley
Performapal Popperup
Poisonous Winds
Power Filter
Psychic Blade
Quiet Life
Runick Allure
Runick Destruction
Runick Dispelling
Runick Flashing Fire
Runick Fountain
Runick Freezing Chains
Runick Slumber
Runick Smiting Storm
Runick Tip
Secret Village of the Spellcasters
Star Blast
Super Hippo Carnival
Super Polymerization
Stoic Challenge
Wave-Motion Cannon
White Veil

And the Band Played On
Anti-Spell Fragrance
Bad Reaction to Simochi
Bad Luck Blast
Banquet of Millions
Blasting the Ruins
Ceasefire
Chain Burst
D.D. Dynamite
Destiny Board
Destruction of Destiny
Destruction on Schedule
Diamond Dust
Dimensional Barrier
DNA Transplant
Elemental Absorber
Floowandereeze and the Dreaming Town
Gozen Match
Grave of the Super Ancient Organism
Gravity Bind
Just Desserts
Kozaky’s Self-Destruct Button
Lose 1 Turn
Lucky Punch
Macro Cosmos
Marincess Wave
Mind Drain
Mistake
Ojama Duo
Ojama Trio
Powersink Stone
Red Screen
Relay Soul
Ring of Destruction
Rivalry of Warlords
Secret Barrel
Secret Blast
Skill Drain
Soul Drain
Summon Limit
Synchro Panic
Synchro Zone
The Monarchs Erupt
There Can Be Only One
Tri-and-Guess
Tyrant’s Throes
Tyrant’s Tirade
Wall of Revealing Light

Limited:
Evigishki Gustraken

Harpie’s Feather Storm