Infinite Arcane Ward stacks - Baldur's Gate 3 (BG3)

Arcane Ward​ is a passive feature of the Abjuration School Wizard, when casting an Abjuration spell, gain a charge in Arcane Ward​ which blocks incoming damage. This feature includes some hidden mechanics and exploits that can cause the stacks to increase significantly.

Important mechanics

• The maximum damage reduction from Arcane Ward​ is always 20, even for a level 11 or 12 Abjuration Wizard with millions and billions of stacks.
• If an Abjuration Wizard rolls an attack that is blocked by a target casting the wizard version of Shield​ , the Abjuration Wizard attacker will lose all their Arcane Ward​ charges.
• Because Arcane Ward is implemented as a condition with a duration, it counts as a condition being applied by the spell cast to charge it. This means that if Metamagic: Extended Spell​ which doubles the duration of any condition applied by the spell is used when casting an Abjuration spell, Arcane Ward​ charge count will also be doubled. 
• Counterspell​ will always restore 3 charges even if upcasted
• Despite being an Abjuration spell and consuming a spell slot, Shield​ does not grant Arcane Ward​ charges

Leveling order

Achieving game breaking amounts of stacks is quite straightforward. The leveling of the build is not crucial; the key is to have at least 2 levels in the Abjuration School Wizard and 2 levels in any Sorcerer. For whole leveling process I recommend using this Abjuration Wizard build.

Setup - Breaking numbers

The usual preperations for achieving higher numbers requires no in-game gear. Only requirements are having a Sorcerer with Metamagic: Extended Spell​. This bug does not require using surfaces or clouds, it works whether the spells are cast by the Wizard themselves, multiclassed with Sorcerer, or by a Sorcerer party member.

Any Sorcerer who uses a damaging spell (which can be affected by Extended Spell) on an Abjuration Wizard while Metamagic: Extended Spell​ is toggled will trigger the bug, but using non-surface or cloud spells is highly inefficient, as it will quickly use up Sorcery Points.

To do this, an Abjuration Wizard must have at least 3 charges of Arcane Ward​, then if a Sorcerer casts a spell which creates a damaging surface or cloud and then toggles Metamagic: Extended Spell​, if the Wizard takes damage from the spell, each time they take damage, the number of charges will decrease by 1 as usual, but then double.

Setup - Limited duration spells

Metamagic: Extended Spell​ which doubles the duration of any condition applied by the spell – is used when casting an Abjuration spell, Arcane Ward​ charge count will also be doubled. This doubling occurs after the cap equal to twice the Wizard's class level is applied, meaning that this can be exploited to gain charges up to four times the class level. 

However, when Arcane Ward has been overcharged in this way, casting any Abjuration spell that would normally charge it without using Metamagic: Extended Spell​ will force it to be capped again at twice the Wizard's class level. This can be achieved most time limited Abjuration spells like Banishment​, Arcane Lock​, Dispel Evil And Good​ or Sanctuary​.

Credits

Special thank you to Meph for introducing me to the Sorcerer extended magic exploit.