According to RegisKillbin, there'll be "a bunch" of balance changes to current Heroes and Treasures.

It's already been confirmed that Fire Drek'Thar will get hit, and probably also Big-Scepter of Summoning decks!

General Updates

All the updates here!
(THERE ARE A LOT)

https://playhearthstone.com/en-us/news/23784368/

A Duels Balance Changes has just rolled out with a server-side hotfix!
• Wildfire and OG Malygos banned;
• Legendary Loot and Unstable Magic moved to UR Pool 2.

https://us.forums.blizzard.com/en/hearthstone/t/patch-2301-patch-notes/84606

48 Voyage to the Sunken City Duels Decks | Weekly Report #155 (12 Win Duels Decks)
https://www.reddit.com/r/HS_Duels/comments/u5nbau/48_voyage_to_the_sunken_city_duels_decks_weekly/?utm_medium=android_app&utm_source=share

Duels Balance Changes!

● Humble Blessings > 4 Mana;
● Academic Research > No more Draw at the Start of the Game + give Empty Mana Crystals;
● Valorous Display > 7 Mana;
● Tempest’s Fury > 4 mana 3/3;
● Power Up! [Hero Power] > Overload 1;
● Scales of Justice > 6 Mana;
● Ol’ Faithful > 4 Mana.

https://playhearthstone.com/en-us/news/23797160/23-0-3-patch-notes

46 Post Nerf Duels Decks | Weekly Report #157 (12 Win Duels Decks)
https://www.reddit.com/r/HS_Duels/comments/ug3ghn/46_post_nerf_duels_decks_weekly_report_157_12_win/?utm_medium=android_app&utm_source=share

80 Duels Decks played in the first week of May | Weekly Report #158 (12 Win Duels Decks)
https://www.reddit.com/r/HS_Duels/comments/ul3zby/80_duels_decks_played_in_the_first_week_of_may/?utm_medium=android_app&utm_source=share

71 Duels Starter Decks played this Week | Weekly Report #159 (12 Win Duels Decks)
https://www.reddit.com/r/HS_Duels/comments/uq3dfh/71_duels_starter_decks_played_this_week_weekly/?utm_medium=android_app&utm_source=share

Duels Balance Changes

Dragon Affinity, Emerald Goggles, and Fire Spells Passives have been nerfed!

(Source)

18 Duels Post Balance Change Starter Decks played this Week Weekly Report #161 (12 Win Duels Decks)
https://www.reddit.com/r/HS_Duels/comments/uvc8j7/18_duels_post_balance_change_starter_decks_played/?utm_medium=android_app&utm_source=share

25 Throne of the Tide Top Decks | Weekly Report #164 (12 Win Duels Decks)
https://www.reddit.com/r/HS_Duels/comments/v5cxjx/25_throne_of_the_tide_top_decks_weekly_report_164/?utm_medium=android_app&utm_source=share