Volzar, the Lightning Rod (ROS021) [Rosetta]

If you control an aura permanent with Sigil in its name, this costs [1 Resource] less to activate.<br>
<br><strong>Once per Turn Instant -- [1 Resource]: Amp X,</strong> where X is the number of Lightning cards you've played this turn. <em>(The next time you would deal arcane damage this turn, instead deal that much plus X.)</em>