This mod contains two new tactical encounters for the Shadows of Amn part of the game. Requires Throne of Bhaal.

Includes Deeper Shadows of Amn, Difficult Brown Dragon, Improved Copper Coronet, Improved Crypt King, Ghost Shadow Dragon, Gnome Fighter/Illusionist Encounter, Grothgar the Red Dragon, Improved Kangaxx, and Curse of the Underground Shade Lord.
The current version is v2.2

In Adventure's Mart speak to the wyvern until you get a new dialogue choice, he will tell you a riddle, the answer will lead you to a pack of really tough battles. Those who survive will get the reward.

This is a mod that changes the Spellhold Dungeon that makes it more fun and challenging for veteran BG2 players.

Although an excellent game, with generally well-rounded battles, some encounters in Baldur's Gate II lack the effort put into so many of the others. Some battles are exquisitely designed, while others seem to have been put together in mere minutes. This mod tries to bring more balance into those lacking battles.

Is the duergar party headed by Ilyich in Irenicus dungeon too easy for you? Are you tired of your failure to defeat the Improved Ilyich from Tactics? Then this is the right mod for you. This mod will automatically install v1.9 of the Detectable Spells pack.

The Spellhold Gauntlet is a series of trials meant to test your limits, both your mettle and your resource management. If you survive you probably have considerable focus of both mind and body. In this chamber you shall be in the center of the room and be continuously set upon by waves of enemies, and you will receive tokens in return for defeating each wave, which can be used for Resting, Items, Scrolls and moving on from the Gauntlet.
The current version is v1.10

If you are up to one of the most challenging and entertaining fights ever put into a computer game, then I encourage you to download this mod. I don't recommend it for people who are brand-new to the Baldur's Gate games or computer games in general. You will never defeat him and I frankly don't feel like listening to everybody whining that they cannot defeat this dragon. Even with my latest enhancements, the dragon is beatable. He is a lot harder to exploit than the original, so you will have to think.

Sword Coast Stratagems II is a collection of mini-mods for Baldur's Gate II, affecting both Shadows of Amn and the Throne of Bhaal extension. Like its Tutu predecessor, SCS II is mostly a tactics mod, intended to make the combats in the game more challenging and interesting. Overall, playing SCS II shouldn't exactly feel like a whole new game - it should feel like the old game, but with your foes acting much more intelligently and realistically, although certain glitches may lead to all enemies in view attacking each other with the equivalent of a +4 longsword of dispelling. This can mostly be avoided by attacking from invisible, ie a rogue backstab.
The current version is v8

The Tactics Mod Pack adds quite a few optional components to BGII. They all aim to make the game more challenging and rewarding by increasing the difficult (and thus the thought required) of encounters.

This mod is a smallish pack of small quests or single fights, which are too small to be released as stand-alone mods. Components range from serious to silly and 4th wall breaking, and from strict adherence to the rules to blatant cheating. Since the installer is WeiDU, you can choose to install all or select individual components. Less serious (or cheesier) components are explicitly marked as such in the readme and in the installer.

This mod adds a turnip golem somewhere in the slums. Where exactly, no one knows, because no one has ever met it... and LIVED! Applying a bit of rudimentary logic will put you on the right track, however. Ask yourself where you would you find turnips in the slums in the first place.
The current version is v1