Baldur's Gate 3 mod adds higher difficulty than Tactician

techradar.com:

A Baldur's Gate 3 mod adds a difficulty higher than Tactician, making the game even harder.

Currently, Baldur's Gate 3 has three main difficulty modes for a variety of playstyles, including Explorer, Balanced, and Tactician. Explorer is tailored for players who wish to play through the game's story without being weighed down by intense combat, while Balanced is as its name states, a balanced experience that juggles gameplay and story and would be considered the «normal» mode difficulty.

Then there's Tactician difficulty. This mode is specifically designed to give players an even bigger challenge. It makes the combat even tougher and gives enemies increased health, while also making other features less fair than other difficulty settings. 

Apparently, some players have found even Tactician to be too easy for them because one user over on Nexus Mods has created a mod that implements another, much more challenging difficulty called Death March Alpha (via PC GamesN).

Death March Alpha — which name derives from The Witcher 3: Wild Hunt's hardest difficulty — «aims to increase the difficulty of almost all combat encounters by adding new enemies, buffing them, expanding their skillsets as well as adding completely new enemy types to challenge you.»

«All changes are seamlessly integrated by going over each fight by hand,» explained modder Lightboom.

Along with a new difficulty mode, the mod adds several new enemy types, including Chemists who have joined the Goblin ranks and use their infusions to buff and support their allies, while also using bombs to kill enemies.

There are Drow Assassins who «watch over certain Absolute plots,» as well as Githyanki Warmages who aid Githyanki search parties and come equipped with a powerful boon.