Bruiser – Renata
To put it bluntly, in the first version of Season 6.5, the Bruiser – Renata composition was the strongest team comp in Teamfight Tactics with both strong attack and defense capabilities. However, with the arrival of version 12.5, this composition has experienced the most significant power drop due to extensive nerfs. Specifically, with the Chemtech trait being nerfed and a series of key units having their damage reduced, the total damage output of this team comp has drastically decreased, and Renata alone cannot carry the team as before.

Moreover, Riot’s rework of Rek’Sai has had a very negative impact on the Bruiser system and has weakened several team comps that relied on it. Specifically, in version 12.5, Rek’Sai received a light rework by removing the ability to steal defensive stats, instead allowing this unit to heal more on targets that have been bitten previously. Clearly, with the healing reduction effects being so prevalent right now, Rek’Sai’s rework has made this unit noticeably weaker, and its mid-game strength has dropped significantly.
Innovator – Kha’Zix
With the absurdly powerful attack damage buff from the Tech Bear, the Innovator composition combined with physical carries proved to be very strong in the previous patch. Since the Innovator team has enough tank units (melee Jayce, Singed), crowd control (Zilean), healing (Seraphine), attack speed buffs, and item holding capabilities (Ekko, Ezreal), building physical carries became exceedingly easy. Riot obviously did not accept this, so they heavily nerfed the Innovator in patch 12.5.

Not only was the Tech Bear’s attack damage buff reduced, but even Ezreal received a nerf, causing his output damage to decrease significantly. Following that, Kha’Zix’s reliable companion – Ekko also received a nerf to his starting energy stats, making it difficult for this champion to snowball with consecutive jumps and critical strikes as before. Perhaps Riot Games is steering the Innovator composition back towards a magic playstyle centered around Seraphine rather than buffing too many things for physical carries.
Mutant
Although not overly dominant, the Mutant composition remains a strong team comp with incredible carry potential from Malzahar. Combined with Rek’Sai’s above-average tankiness, the Mutant composition inadvertently became extremely strong, and its early game weaknesses completely vanished. However, this changed when Rek’Sai was nerfed due to the Bruiser team being too strong, resulting in that adjustment also affecting the strength of the Mutant composition.

Additionally, the damage output that Malzahar can inflict has been nerfed, making the Mutant team much harder to play effectively in the late game. Essentially, the nerfs targeting both Malzahar and Rek’Sai will reduce the mid-game strength of the Mutant team, and you will easily find yourself lacking damage. Therefore, this composition will heavily depend on whether you can roll for Malzahar or especially a 3-star Cho’Gath instead of “surviving well” and leveling up to 8 easily as before.