Film thickness and material: Thicker isn't automatically better, but premium card sleeves tend to land around 90-110 microns for outer sleeves
Souls of the Forgotten Souls of the Forgotten is a scary card not only because of its appearance, but also because of what it represents
Your winning line of play is simply any sequence of sufficiently efficient, self-replacing spells, followed by a storm spell
Neat synergies here, even if there are some immediately obvious infinite combos with Cayth
Overall, it's not a crazy reward for unlocking four very difficult to obtain pieces of card art, but it's certainly setting you up for future pack openings and trades
For any card printed since 1998, you have two clear indicators: The Set Symbol Color: The most immediate visual cue is the expansion symbol, located on the right side of the card, between the art and the text box