Volcano Hellion has echo, where X is your life total. (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When Volcano Hellion enters the battlefield, it deals an amount of damage of your choice to you and target creature. The damage can't be prevented.
2/1/2007 As Volcano Hellion’s enters-the-battlefield ability resolves, you choose a number. Volcano Hellion deals that amount of damage to you and to the targeted creature. You may choose 0.
2/1/2007 Volcano Hellion’s echo cost constantly changes; it’s not locked in when it enters the battlefield. The echo cost you pay is equal your life total as the echo triggered ability resolves.