Changeling Outcast: This is an unblockable 1/1 that can't block. That part doesn't matter because you usually won't have any reason to block with it. It's a shapeshifter so it has every creature type. After it gets bigger from other creatures like card:lord of unreal it can present a large threat if left not dealt with.
Universal Automaton: The pro on this card is that it only cost for a 1/1 shapeshifter. The con is that by itself it doesn't really do anything. If you have no cards that pump it or give it abilities it will just be a 1/1 creature for one mana.
Unsettled Mariner: It's a shapeshifter, it gives your stuff hex proof unless your opponent pays one mana, and it's a 2/2 creature. It's a very good card and it's even played in other decks besides shapeshifter tribal.
Mirror Entity: In some scenarios this is the last card you want to draw while in others drawing it will win you the game. Mirror Entity allows you to pay X mana and have all of your creatures have base power and toughness X/X until end of turn and it makes them all creature types. This works best as a late game finisher. You usually are going to wait until a turn after you've played Mirror Entity to activate its ability. One exception is if you have a Cloudshredder Sliver on the battlefield ready to give all of your creatures flying and haste.
Valiant Changeling: Valiant Changeling is an incredibly good card that's usually going to be a 3/3 double striker for just . It states that it cost one less mana to play for each creature type among creatures you control. That means if you control a card with every creature type it will cost 251 less generic mana to pay. Having double strike means that it will deal a lot of damage fast if it's being pumped up. This is a very fun card to play on turn 2.
