Plasm Capture
Instant
Counter target spell. At the beginning of your next precombat main phase, add X mana in any combination of colors, where X is that spell's converted mana cost.
"Everything serves a purpose. Even you." —Vorel of the Hull Clade
Illustrated by
Dragon's Maze#91RareEnglishLegality
Rulings
Apr 15, 2013
If the countered spell had 
in its mana cost, include the value chosen for that X when determining how much mana to add to your pool. For example, if you counter a spell that costs 
with X equal to 5, you’ll add six mana to your mana pool.
Apr 15, 2013
Your precombat main phase is the main phase that happens immediately after your draw step, not any other main phase.