The TTAPU espionage satellites ground scans have detected large amounts of uranium 238 under the Equestrian forests, which, of course, the ponies are mining to defended their nation. This shall not succeed, not on the Triforce Alliance's watch. Anyway, a new kind of fungus has been genetically engineered by the TTAPU. It is a painless, but quick, killer, and it's symptoms are only noticeable through thorough diagnosis. Otherwise, it is unknown to the victim, let alone anyone else.
The fungus is called the Termination Cometh. Under a microscope, it's buds are very small blue tree-like creatures. It slowly secretes painkillers before digesting the area that has been neutralized. To avoid notice, the Termination Cometh has been designed to digest the victim from the inside out, so only when the victim dies it is revealed what it's executioner was.
The TC should arrive in a crash pod in Ponyville in 16.17 hours.