Vat's Green Eyes of Truth

You point a finger at a target in range. Your eyes glow a faint green and green and black lines that only you can see start to creep up around the target's body, outlining its weak spots and providing insight into its defenses. For the duration of the spell, provided you don't lose your concentration nor do you attack another target, every attack you make against the chosen target gains the following effect: when rolling to hit, instead of following the usual rules roll 4d20. Now, you may use the highest number as the result of your hit roll or you may use the lowest number times two. If you choose the second option and the resulting number is over 20, you may also add 1d4 of extra damage to the attack if it hits. No modifiers or rerolls may be applied to any dice no matter which one you choose.