Abyss Foscari Achievement in Vampire Survivors

Refer to the roadmap for the progression of how to unlock Keitha.

With Keitha, start up a run on Lake of Foscari. You'll need to reach the Seal with her evolved Flash Arrow (refer to Ophion (5G) or the roadmap for how to evolve all the weapons). The Seal is located in the northeast of the map, and is marked with a question mark, but to get there you need to head northwest. Basically, you're going to go the same direction you went to get to the coffin, and from there you can head east to get to the question mark. The Seal is a giant gem. Face it so you shoot it with a Flash Arrow, which will break it, immediately unlocking this achievement and starting you on a new stage, Abyss Foscari.