A deck can have any number of cards named Rat Colony
Cards that add +1/+1 counters are getting much more efficient, so between Innkeeper's Talent and Tribute to the World Tree, you can have a pretty powerful Warcaller leading your troops
The biggest hurdle is that 4 cost to play it
I wont be providing a TL;DR: other than to say that Backgrounds are incredibly powerful and that, if you highly disagree with anything I say, consider if it has Choose a Background printed on it
Thunderbreak Regent Thunderbreak Regent is an absolute nightmare for opponents who like targeting your creatures
Rank: Fun Gogo, Mysterious MimeGogo, Mysterious Mime Gogo seems fun in combination with powerful attack triggers from cards like Etali, Primal StormEtali, Primal Storm and Godo, Bandit WarlordGodo, Bandit Warlord