What multiclass options work well with a Barbarian in Baldur's Gate 3?

Multiclassing a Barbarian in Baldur's Gate 3 can create a powerful and versatile character, but it requires careful planning to ensure the build remains effective. Barbarians are known for their high durability, rage mechanics, and melee prowess, so multiclassing should complement these strengths without diluting them. Below is a detailed guide on how to approach multiclassing with a Barbarian, including mechanics, strategies, and tips.

1. Detailed Explanation of the Mechanics Involved:
Barbarians rely on their Rage ability, which grants them resistance to physical damage, bonus damage on melee attacks, and advantage on Strength checks and saving throws. This ability is central to their effectiveness in combat. When multiclassing, you need to ensure that the new class synergizes well with Rage and doesn't interfere with its activation or benefits. Additionally, Barbarians are Strength-based characters, so multiclassing into a class that also benefits from high Strength or Constitution is ideal.

2. Step-by-Step Instructions or Strategies:
A common and effective multiclass option for Barbarians is the Fighter. Fighters offer additional combat versatility, Action Surge, and Fighting Styles, which can enhance a Barbarian's melee capabilities. Here's how to approach this multiclass:
- Start as a Barbarian for the first 5 levels. This gives you Extra Attack, which is crucial for melee damage output, and access to your subclass features.
- At level 6, take your first level in Fighter. This grants you a Fighting Style, such as Defense for +1 AC or Great Weapon Fighting for better damage with two-handed weapons.
- Continue leveling Fighter until you reach level 3, unlocking a Fighter subclass. The Champion subclass is a good choice for its improved critical hit range, which synergizes well with Barbarian's Reckless Attack.
- After reaching Fighter 3, you can either continue leveling Fighter for more feats and abilities or return to Barbarian for higher-level features like Brutal Critical.

Another strong option is multiclassing into Rogue. Rogues offer Sneak Attack, Cunning Action, and expertise, which can make your Barbarian more mobile and versatile. Here's how to approach this multiclass:
- Start as a Barbarian for the first 5 levels to gain Extra Attack and Rage.
- At level 6, take your first level in Rogue. This grants you Sneak Attack, which can be used with finesse weapons like rapiers or shortswords, even if you use Strength to attack.
- Continue leveling Rogue to gain Cunning Action for bonus action Dash, Disengage, or Hide, and expertise in skills like Athletics or Stealth.
- At Rogue 3, choose a subclass. The Thief subclass is particularly strong for its additional bonus action, which can be used for an extra attack or mobility.

3. Important Tips and Considerations:
- Avoid multiclassing too early. Delaying Extra Attack or Rage progression can significantly weaken your character in the early game.
- Consider your ability scores. Multiclassing into a class with different primary stats, like Wizard or Sorcerer, is generally not recommended for Barbarians.
- Be mindful of armor restrictions. Barbarians benefit from Unarmored Defense, so wearing heavy armor can negate this feature. Stick to light or medium armor if multiclassing into a class that doesn't rely on Unarmored Defense.
- Plan your feats carefully. Multiclassing can delay access to Ability Score Improvements or feats, so prioritize those that enhance your build, such as Great Weapon Master or Sentinel.

4. Common Mistakes to Avoid:
- Multiclassing into too many classes. This can spread your abilities too thin and make your character less effective.
- Ignoring synergy between class features. For example, multiclassing into a spellcasting class like Cleric or Druid can be problematic because you cannot cast or concentrate on spells while raging.
- Overlooking the importance of Extra Attack. Delaying this feature can significantly reduce your damage output.

5. Advanced Techniques or Optimizations:
- Combine Barbarian's Reckless Attack with Fighter's Action Surge for devastating burst damage.
- Use Rogue's Cunning Action to position yourself strategically in combat, ensuring you can always reach your target.
- Consider taking the Mobile feat to enhance your mobility and avoid opportunity attacks, making you even more effective in melee combat.

6. Related D&D Rules and Mechanics:
- Multiclassing in Baldur's Gate 3 follows the same rules as Dungeons & Dragons 5th Edition. You must meet the ability score prerequisites for both your current class and the class you want to multiclass into.
- Rage prevents you from casting or concentrating on spells, so multiclassing into a spellcasting class is generally not recommended unless you plan to use spells outside of combat.

7. Specific Examples and Scenarios:
- A Barbarian 5 / Fighter 3 build can use Reckless Attack to gain advantage on attacks, combined with Action Surge for an additional action, allowing for up to four attacks in a single turn. This is particularly effective against tough enemies or bosses.
- A Barbarian 5 / Rogue 3 build can use Sneak Attack in combination with Reckless Attack to deal significant damage while maintaining high mobility and utility with Cunning Action.

In conclusion, multiclassing a Barbarian in Baldur's Gate 3 can create a highly effective and versatile character, but it requires careful planning and consideration of class synergies. By following the strategies and tips outlined above, you can create a powerful multiclass build that enhances your Barbarian's strengths and adds new dimensions to your gameplay.