They all can be evoked for two mana, and the color you choose will determine the ability you get
Plus it may give you a deeper understanding of the game and teach you about the scenarios where there are exceptions and how to identify them
But you can still cast these abilities at instant speed with enough flash enablers
Before the game begins, you build a Mercenary stack of dorks
Theres a kind of fluency to so many of the cards that makes fans like me stop and say, Oh they get who Aerith really is with this ability! Cards tell stories that fans remember from the games while not going so far as to alienate those unfamiliar
Thistledown Liege is clearly the worst of the lieges, as it is merely a 1/3 for 4 mana, and its keyword, flash, is useful, but only once, so I question how WotC could have designed this creature