It is part of the EX Series
You could be punished for merely hurting a cat, and tortured or even killed for murdering one
During your turn, spells you cast from your hand with mana value X or less get cascade, where X is that total life lost
Basically, according to Wizards ' own thoughts back in 2015 and the consensus view of the community, the London mulligan rule seems likely to power up two of the most problematic and least liked aspects of the Modern format, and this doesn't even take into consideration that certain cards or decks can directly abuse the rule (most commonly cards or combos that actually want you to have fewer cards in hand, like Restore Balance or Ensnaring Bridge, both of which happen to win by making the opponent unable to play a full game of Magic or, in the case of Restore Balance, any form of Magic at all)
Its incredibly difficult to predict how good this equipment planeswalker is, but if Wizards has put their force behind it to make it a headliner, expect it to perform well