Mawile 17/108 is a Rare card and belongs to Rare cards of Ex Power Keepers series
30% of the time in Modern Horizons 2 Set Boosters, you will instead get a rare or mythic raremaybe even with a showcase sketch treatment, showcase retro frame, or borderless treatment
You can play this card in tanky lineups (maybe find a place for it in your new Tera decks, even), or pair it with Energy recycling decks like Gardevoir ex to counteract its Energy trashing
The idea of the rule is simple: in the wake of fan-favorite LSV losing in the Top 8 of a recent Pro Tour after mulliganing to four in the last game of the finals, the London mulligan is designed to decrease the pain of mulliganing and the number of non-games that happen as the result of one player having a hand that simply doesn't do anything (like no lands, for example)
And even if you aim to extend the game far beyond the next turn, youre almost always trading up on mana while remaining even on cards (and, in fact, seeing deeper into your library)