Another distinction of Skill Cards from other cards is that the card backing is different from the standard card backing, featuring some artwork of the character associated with the skill and text describing its activation conditions
Pair Wrenn with a card like Dryad of the Ilysian Grove and the ramp gets steeper
When played, Yogg-Saron casts a random spell with random targets for every spell you previously played in the game, resulting in utter chaos from things like Yogg destroying your opponent's board, Pyroblasting you in the face, drawing a bunch of cards, betraying you and casting spells for your opponent, summoning a bunch of tokens, or even instantly killing himself
In Mardu there are 48 Slivers with power two or less, so tons of creatures too recur
The Japanese foil layering makes every flame pulse with depth and motion, giving this card a cinematic presence