Board Thread:General Discussion/@comment-35806478-20190408161347/@comment-32182236-20190426111951

Before Sans, every kill was from Frisk. So Chara wouldn't actually be gaining that much power. When they did finally take control over Frisk, Sans, Asgore, and Flowey were killed.

Now, we don't actually know how to calculate execution points. It seems to be both based on how good of a monster the victim was, and its strength, because the EXP you gain slowly grows over time, but it also flickers a lot depending on the kind of monster you killed. (For example, Jerry's only worth 1EXP.)

As we know from the Photoshop Flowey fight, Flowey is at LV9999. While we don't know how he did this, he did this nonetheless. He's also Asriel, who used to be Chara's best friend, and was the nicest monster in the entire Underground, but now cursed to not feel anything again.

So it could seriously be argued that killing him lead to a MASSIVE influx of execution points, perhaps even enough power to give Chara the ability to do what they did.