Time ram
From Tardis Wiki, the free Doctor Who reference
Time Ram is the name given to what happens if two TARDISes attempt to occupy exactly the same time and space. (DW: The Time Monster)
It can be narrowly avoided by the two TARDISes materialising within each other. (DW: The Time Monster, Logopolis) This happened to the Tenth Doctor and the Fifth Doctor. The Doctor, describing it, said it would cause a black hole strong enough to destroy an entire universe. (DW: Time Crash)
The Sixth Doctor performed a time ram against the remains of Iris Wildthyme's TARDIS at the center of a dimensional nexus. Local conditions limited the effects to merely eliminating some possibilities from reality, but the force was still enough to destroy the rest of Iris' TARDIS. (BFA; The Wormery)
