Ill-Timed Explosion

The drawback pays for the sweeper, and the payment schedule is the whole trick. Draw two, unconditionally, then decide whether to discard two: the discard is optional, and only if you take it does the board wipe fire, with X set to the greatest mana value among the cards you pitched. That coupling is what makes the spell interesting to sequence, because the size of the Explosion moves with your hand and stays entirely in your control. Pitch two lands and X is zero, so nothing dies (lands are mana value 0); feed it a six-drop and every creature takes six, enough to strip that much toughness off the whole board. The card advantage arrives no matter what, so even when the sweeper mode is wrong (nothing worth killing, or nothing worth losing) you still bank two cards; the reset rides along as an option you can decline. What keeps the ceiling honest is that the damage hits every creature and the payment comes out of your own refilled hand: you cannot scale the blast without spending the resources you just drew, and the biggest wipes cost you the best cards to throw away. It belongs to the family of blue-red spells that launder card advantage into battlefield pressure, but the mana-value dial is the wrinkle. The same four mana buys a two-card draw with a shrug of a rider, or a full board reset, depending on what you are willing to burn to power it.