Here re twelve absolutely unstoppable monsters (around Tarrasque level) that would cause worldwide devastation if a band of valiant heroes do not stop them in time. Usually, these forces of nature are locked away and the heroes may be able to keep the door of their prison closed or sometimes, they may have to come up with another way of stopping the creature (like there are ways of stopping the Tarrasque). However, as H.P. Lovecraft, Peter Davill-Evans and Dave Morris has shown us, entities this powerful cannot be destroyed for good.
Even smaller dragons cause havoc in the lands of humans, but this one really takes the biscuit. It fits the criteria of dragons - flying and firebreathing but it is also larger than most dragons and it can attack as soon as it is summoned, trampling anything in its path. If by some miracle, it is dealt lethal damage, if it has access to some green mana, the mana of nature, it can regenerate itself so it will start the whole cycle of destruction again.
Just as big as the Hellkite Overlord and capable of damaging any number of opponents with its multitude of heads. This monster not only causes massive damage. It causes massive damage to everyone at once so even ganging up on it isn't that effective. Good luck.
This creature is so big that it displaces enough water to flood the rest of the lands. It also surrounds you with plenty of water so that creatures who cannot traverse it or fly over it cannot attack you. what is more, it is impossible to defend against it if you are on an island so it will be coming to swallow you up soon.
This is the beast of beasts. It is huge and can attack and summon another beast just like it in the same turn. You aren't just dealing with one massive force of nature - you are dealing with a steady stream of monsters all just as hard to kill and there will be no end to the assault unless you kill the original Godsire.
Avatar of Slaughter
This is a huge nasty creature, but the death and destruction it will cause is nothing compared to the damage caused by the rage it incites. It makes everyone simultaneously bloodthirstry and deadly and they will not stop until they are dead or all of their enemies are. This creature can start a huge world wide bloodbath. Beware its release.
This creature is the physical manifestation of the darkest thoughts of twisted wizards. Its presence is enough to wipe your mind of all of its spells and more through the sheer terror of its appearance. Left mentally defenceless, this nightmare will crush you like a bug.
The world itself is angry and it is now fighting back. Nature herself has assembled an elemental to destroy anything that is not like itself and it will not stop until the artifice and corruption that blights it has been layed low. Cheap tricks and dark magic are not going to stop this elemental.
Demon of Death's Gate
Mighty demons require mighty sacrifices. You can summon this demon with mana or you can summon it with blood. Wither way, it will crush your enemies.
As well as being a powerful creature, this archon will definitely avenge you by reflecting any hostile magic against its perpetrator.
It's huge. It can't be destroyed and it will kill you with its corrupting disease. Only a sick and twisted world could come up with such a sick and twisted artefact.
Marit Lage is imprisoned under the ice. If it is released, its 20/20 flying indestructable form will make short work of even the most powerful planeswalker.
Whatever you do, make sure that the ice stays thick.
Emrakul, The Aons Torn
Finally, we have a huge beast that goes further than the previous eleven. They were only content to destroy a world. This thing destroys worlds. It is almost unstoppable. It is huge. It flies. It can manipulate time so that it seems to move twice as fast and every time it attacks, it devours creatures or even lands. Finally, it will never truly die. If the Eldrazi come for your plane, you find a way to get off that plane. Or you try to imprison them. or you get devoured.
Only one of these creatures is enough to overturn the world, but they can do so in many different ways.
Until next week...