From the moment Teamfight Tactics Season 3 was launched, the incredibly dominant power of Gangplank was recognized due to his massive damage from abilities, his ability to stun widely from the Shattering system, and those overpowering upgrades. Therefore, in the early phase of this season (except during the prevalent hyper-roll period), Gangplank was almost the strongest unit in the game.

Therefore, in the upcoming mid-season update, not only will new traits and units be introduced, but Riot Games will also focus on balancing the units and items that are too overpowering or have unreasonable power, among which Gangplank is the unit that will be heavily nerfed. The specific changes from the PBE server are:
System
If you sell a unit that is not a 1-star and 1-cost, you will be penalized 1 gold (for example: selling a 3-cost 2-star unit will return 8 gold instead of 9 gold).
The appearance rates of 1/2/3/4/5-cost champions at level 9 have changed from 10/15/25/35/15% to 10/15/30/30/15%.
Balance Changes
Giant Slayer: Damage cap per hit increased from 1500 to 1750.
Dark Star: Additional AD and AP from each fallen allied champion reduced from 8/20/30/50 to 8/16/24/32.

Mercenary: Gangplank’s skill width reduced when purchasing the “Expansion” upgrade.
With the excessive popularity of the Korean Jhin – Gangplank composition, being stunned widely by Gangplank is a common occurrence in the game. Moreover, the only item that counters control effects, the Quicksilver, only provides for 1 unit, while Gangplank’s skill is wide-ranging, making it normal for the entire battlefield to be “bombed”.
With the above nerfs, Gangplank’s opponents will have a bit more space, albeit very small, to prevent their units from being controlled and find a way to take down this 5-cost pirate.

War Machine: Healing/damage capability reduced from 70/150/300/600 to 70/150/275/500.
Kog’Maw
Base health reduced from 550 to 500.
Bonus attack speed from skill reduced from 90% to 80%.
Urgot
Energy reduction from ultimate ability decreased from 10/30/100 to 10/20/100.

Three consecutive nerfs to the key units of the War Machine trait illustrate just how powerful they are on the test server. Perhaps Riot Games will need to nerf this trait in the long term before its official launch because their nature is too strong when they have additional damage, healing, and the activation threshold is too low (2/4/6/8 units).