D (Double)

Strategy and Synergy
This is an excellent upgrade on any spell in the game, but its cost can be prohibitively high on expensive spells like, , or. Carefully consider whether you want a 6+ spell in your deck before taking this effect on a 4+ Mana spell.

Double is an easy upgrade to find on any spell that doesn't deal damage or fire projectiles, because they are ineligible for several other upgrades like or. Consider using your upgrades on cheap utility spells like, , , , or - you'll frequently get Double on your first attempt, and it makes them even more efficient than they already are for only 1 extra Mana.