Subcritical Uranium-235

As an additional cost to cast pay 10 life.
Subcritical Uranium-235 enters the battlefield with
3 meltdown counters.
At the beginning of your upkeep remove a meltdown counter. When you remove the last meltdown
counter Subcritical Uranium-235 deals
2 million damage to every creature, planeswalker,
and player, then exiles itself.
A Solid 20,000 KG block of subcritical uranium-235 is necessary for adequate home defense