Baldur's Gate 3 speedrunners have already been achieving ridiculous times largely by abusing Shadowheart, but a new indignity inflicted upon everyone's favorite moody cleric has brought that world record down to under 20 minutes.
Shadowheart was already a centerpiece of many Baldur's Gate 3 speedruns thanks to a trick called Shadowbox. Basically, you recruit Shadowheart, kill her, stuff her corpse in a box, and take advantage of a glitch to send that box careening to the end of the current area. If you just want to reach the credits - as in the game's Any% category - you can take advantage of this trick to set Gale against the Elder Brain at the end of Act 2 and explode, reaching the credits in three minutes and 31 seconds as of the current world record.
But if you want to truly complete the game by beating Act 3 and reaching the true ending, there's a lot more work involved - including the fight against Ketheric at the end of Act 2. Runners of the Any% All Acts category have recently discovered that the most efficient path to defeating Ketheric is to give Shadowheart a few levels in druid, make her turn into a bear, cast enlarge on her, and then make her new 10,000 pound form jump on Ketheric to deal over 100 damage and kill him in one shot.
This technique has been used to set several new world records over the past several months, but on January 25, a runner named Mae became the first to take that record under 20 minutes. You can see that world record in full above, but if you want to know how it's done - including all the tricks necessary to survive Act 3 - I'd recommend instead watching Mae's AGDQ run of Baldur's Gate 3, where she breaks down all the techniques used to bust the game open.