Mana surge is a game mechanic that doubles the mana you get from a match. The mana surge chance is called mastery. If you make a 3-match and you get a mana surge, you’ll get double mana (6 mana instead of 3). 4-matches never produce mana surges. 5+ matches always trigger mana surge for 10 mana. Any other mana bonuses are added after the mana surge (so bonuses are not doubled). Note though that you don't get mana surges from 4+ matches.