When you're as limited as you are on spell casts in Baldur's Gate 3, sometimes you need a bit of leg to stand on to get through the game's hardest encounters. Upcasting is such a leg, and a powerful tool when used tactically; knowing when and where to use it can save your party. Here's everything you need to know about Upcasting.
How to use Upcasting in BG3
Upcasting in Baldur's Gate 3 is the act of casting a lower-level spell than the spell slot you're using. Due to the limitations of spells, it may seem like a waste to cast a level 2 spell with a level 3 spell slot. In a lot of cases, it is, but not every situation calls for more powerful spells. In fact, just because a spell is of a higher spell level, doesn't necessarily make it more potent.
For example, let's say you are surrounded by a pack of Drow warriors, and they all have an Attack of Opportunity on you. You're a squishy Wizard who has run out of level 2 spell slots and, therefore, cannot cast Invisibility to escape. However, you have one more level 3 spell slot that is unused; this is a situation where you would want to upcast Invisibility.
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In a similar fashion but a different scenario, you've stumbled across a clan of hungry gnolls, freshly birthed from the guts of a hyena pack. You've got the drop on them, and they are clustered together. Perfect. A Fireball will do the trick, but you don't have any more level 3 spell slots to cast it with. As with the previous scenario, you do have a level 5 spell slot that has thus far gone unused. Here, you can use upcasting to invoke Fireball with the level 5 slot.
Some spells are actually empowered by upcasting, gaining additional effects or potency depending on what level spell slot is used.
So, as you can see, upcasting can win seemingly impossible fights; just make sure you use the tool at the right time.
For more quality guides and useful information relating to Baldur's Gate 3, check out How to get rid of Bloodless in BG3 right here on Pro Game Guides.