The Clash Pack doesn't impact the legality for the cards at all. The shooting star growth expression can be used for advertising cards, in this instance cards with an alternate art from their original printing. Therefore as an example even though the Whip of Erebos is printed within product with a brand new art and growth symbol it will nonetheless rotate regarding Standard when Theros does in about a few months, alongside just about any cards from Theros block. The cards from Khans and Fate Reforged would then turn down next year in spring.
The biggest thing to remember as to what determines the legality of cards in traditional is really what ready these were imprinted in. And supplemental products like Clash Packs, Duel Decks, and/or Commander porches cannot change something appropriate at all. However you can use any printing of a card provided it really is legal, in order to use as an example Smite the Monstrous ended up being printed in Khans of Tarkir and Innistrad, and you will utilize either backup inside standard deck.