Baldur's Gate 3 provides players with a number of difficult choices as they play through the game. For the most part, these choices affect story outcomes or other characters' opinions of the player, but some can change the lives of NPCs in the world. Shadowheart is one such NPC whose livelihood depends entirely on the player's decisions.
Throughout their time with Baldur's Gate 3, Shadowheart will present herself as a potential party member several times. She can be a bit abrasive, but most players choose to take her on as a party member. As a cleric, she's very useful to have around, and her Half-Elf lineage gives her access to darkvision as well.
Despite all of this, some players are curious to find out what happens to Shadowheart if they refuse to join up with her at any point in the story. Unfortunately, things don't go well for her, and the player is eventually forced to kill her by the end of it.
The first chance players get to recruit Shadowheart is at the entrance to the Dank Crypt, but those wanting to try this outcome out should turn a cold shoulder towards all her advances. Insisting to go separate ways will eventually see Shadowheart agree, at which point she'll next be seen in the Druid Grove. Here again the player can leave the conversation without adding her to the party. The next time players meet Shadowheart, she will be acting strangely, something the player's character notices almost immediately.
It's revealed through this dialogue that the parasite in her mind is driving her crazy, constantly telling her to find the player and kill them. During the conversation, Shadowheart makes a comment that the whispers she hears are quieter when she's near the player, perhaps explaining why she doesn't go crazy if the player does add her to the party. At any rate, she eventually attacks the player, a course of action which ends poorly for her. Killing her does grant the player some loot, including the Mysterious Artifact, but it's a sad ending for one of Baldur's Gate's potential companions with an interesting backstory.
Unless attempting to do a run with no companions whatsoever, it's advised that players add Shadowheart to their party at the first opportunity. As previously mentioned, her abilities can be extremely useful (especially early on), and her quest is rather interesting as well. Her fate is tied to the player's decisions, so choose wisely.
Baldur's Gate 3 is available now on PC and Stadia.