The Hall of Wind is a weekly Thursday dungeon. You can get Wind Essences here(Low,MID and High). The guardian of wind has excellent recovery. You will need the heal recovery de-buff to stop his healing. B7 and higher has a better chance of dropping better essences.

Stage | Cost | Boss Level
B1 | 4 | 8
B2 | 4 | 10
B3 | 5 | 15
B4 | 5 | 20
B5 | 6 | 30
B6 | 6 | 40
B7 | 6 | 50
B8 | 7 | 55
B9 | 7 | 60
B10 | 7 | 65

The Guardian of Wind has the following skills:

Dead Man’s Purification – Attacks all enemies and stuns them for 1 turn by chance. The damage increases as fewer enemies stand.
Death Glare – Burns Enemies with a cursed glare and inflicts Continuous Damage for 3 turns with a high chance. (Reusable in 4 turns)
Annihilate (Passive) – Get an extra turn if enemy falls. [Automatic Effect]

The left crystal from B1-B5 recovers a percentage of the his HP while from B6 to B10, it recovers ALL of his HP.

DROPS YOU CAN EXPECT

Unknown Scrolls – The higher you go, the number of scrolls you get increases
Wind Essence(Low) – Drops often in the lower stages(B1-B5). At higher levels, it drops more in quantity.
Wind Essence(Mid) – Drops from B2 onwards
Wind Essence(High) – Drops from B4 onwards and it is very rare
Mystical Scroll – Rare drop
Yellow Angelmon – Rare drop
Rainbow Angelmon – Rare Drop
Secret Dungeon Monster – Could be any 2-3 star fire monster

STRATEGY GUIDE FOR HALL OF WIND

Bring monsters with HP recovery debuff. Here are a few:

Colleen(Fire Harpy)