If Clever Impersonator enters the battlefield as a copy of a planeswalker, it will enter the battlefield with a number of loyalty counters on it equal to the loyalty printed in the lower right corner of the planeswalker card
Even in a depowered deck, you can find Salt Marsh, Jwar Isle Refuge, Frost Marsh, and Secluded Glen to make the other colors in a deck built around The Mimeoplasm or something
Barrets attack trigger is fine, but its little more than a nice bonus that can come up every so often
The other idea was building Mardu Goblins, and Neriv can act as a combo finisher with General Kreat, the Boltbringer or Pashalik Mons and a sac outlet
The human berserker is a three-drop 3/2, who exiles the top card of that players library when Boast is activated