When you sit down to play a social game of Magic, it can feel really bad when someone is playing cards that proactively keep you from being able to do your thing
Lines of 45 minutes or more are being reported at some locations, which tells you two things: the card is drawing real foot traffic, and supply is getting hit hard
Then, each Rat we control gets +1/+1 for each fellowship counter on the banner
Looking at one of the games most powerful colors: Blue
It may also be that the arrival of this Secret Lair has boosted players' overall interest in the cat MTG creature type, and these players - perhaps those who missed the boat on the Secret Lair - are now interested in building an Arahbo deck instead
When Themberchaud enters the battlefield, he deals X damage to each other creature without flying and each player, where X is the number of Mountains you control