Boppenheimer's Ballistic Missile

You create a magical siphon around the Delayed Blast Fireball, drawing in massive amounts of power whilst stoking the flames to a temperature hot enough to ignite nuclear fusion, then speak the name of a creature or place you wish to see destroyed and release the spell. The empowered fireball then flies from your hand towards the named creature or place, moving at a rate of 1000ft per round and typically travelling in a ballistic arc (though it will fly higher or lower if need be to avoid obstacles), and upon striking the target it explodes for 10d12 radiant and 10d12 force damage in a 50 foot radius (halved on a successful Constitution saving throw). This damage is tripled against objects, and any object reduced to 0 hit points by this spell is obliterated beyond any hope of repair. If the target is on another plane of existence the spell flies towards the last location they occupied on the caster's plane, or if they have never been on the caster's plane, a target is named that does not exist, or the target is warded against divination magic the spell flies high into the air and detonates. While it is travelling the spell can be stopped, either by a successful casting of Dispel Magic, which causes it to fizzle out harmlessly, or by attacking it (it is a tiny object with 20 AC, immunity to poison and psychic damage, and 1 hit point, which moves fast enough to not provoke attacks of opportunity), which causes it to detonate at its current location.

However, when the spell is cast as a ritual (which still requires expending a 9th level spell slot), it can be empowered further; for each 10 minutes after the first spent casting, the spell deals an additional 1d12 radiant and 1d12 force damage, and gains an additional 10ft of radius when it detonates. There is no known limit to how greatly the spell can be empowered in this way, but doing so causes a tremendous disturbance to the Weave, and the vortex of magical energy this casting creates can be felt even over great distances. After the first 10 minutes any creature capable of spellcasting can detect the disturbance from a distance of 1 mile, and knows the location of the caster with a DC 12 Wisdom (Perception) check and the spell being cast with a DC 18 Intelligence (Arcana) check. This distance increases to 5 miles after 20 minutes, 25 miles after 30, 100 miles after 40, 1000 miles after 50, and unlimited, even on other planes after an hour. Due to the immense destructive potential of this spell it has been banned by most nations and mages guilds, with even those who don't outright forbid its use strictly regulating it, so any attempt at a lengthy casting will no doubt see interference from outside forces, and while performing the ritual the caster is unable to take any actions, bonus actions, reactions, or legendary actions without breaking their concentration. Thus, while its theoretical potential is limitless, its practical potential is far less without an entire army to guard the caster against those who wish to see the casting stopped.

- "I am become death, blower of things up" - Boppenheimer von Fiddlesworth III, deranged gnomish artificer and convicted war criminal