Coldkiller X is a potent cold medicine made by the Tenkai Group pharmaceutical institute.
- Main article: Turnabout Memories
While they were both studying at Ivy University, Dahlia Hawthorne attempted to kill Phoenix Wright with his own bottle of Coldkiller X by mixing in some poison she had stolen from the pharmaceutical department. Her reason for doing so was in order to regain her bottle necklace, which was evidence from her poisoning of Diego Armando.
- The medicine is known as "Coldkiller Z" in the Japanese versions of Phoenix Wright: Ace Attorney: Trials and Tribulations and Gyakuten Kenji 2.