Double

Double is a keyword action formally introduced in Dominaria for <c>Grunn, the Lonely King</c>. 
==Description==
Double multiplies certain characteristics or conditions by two. 
Doubling has existed informally as early as Fifth Dawn with cards like <c>Doubling Cube</c> and <c>Solarion</c>.
Doubling may be applied to:
*Damage (e.g. , )
*The number of counters (e.g. <c>Deepglow Skate</c>, <c>Kalonian Hydra</c>)
*The amount of each type of mana in your mana pool (<c>Doubling Cube</c>)
*The amount of mana that permanents you control produce ()
*Power and toughness (e.g. <c>Grunn, the Lonely King</c>, )
*Life total (e.g. <c>Beacon of Immortality</c>, )
*X Values (<c>Unbound Flourishing</c>)
==Rules==
==Trivia==
*<c>Nyxbloom Ancient</c>, , <c>Jeska, Thrice Reborn</c>, <c>City on Fire</c> and <c>Fiery Emancipation</c> triple effects. 
*Effects that double power and toughness or +1/+1 counters exist primarily in green, although power/toughness doubling also exists on some red cards. In particular, six green cards associated with the Quandrix college have doubling effects, to flavorfully complement its mathematical theme.
**Effects that double damage, on the other hand, exist exclusively in red.
**Effects that double life total exist only in white.
*Mark Rosewater loves to design doubling mechanics. 
**<c>Maro's Gone Nuts</c> is a Mystery Booster test card that spoofs this. It doubles any effect that doubles (it quadruples).
==References==