Why is now the best time to start playing? Not only will Witchwood's 135 new cards be viable for the longest time (two years) of all of 2018's sets, but the whole game is in flux as old deck archetypes become obsolete. The turnover is a great period to experiment as players try out new strategies before the meta settles.
Like other expansions, Witchwood also brings new card types. The first, Echo, lets you play copies of the same card but only on that turn, letting you plunk down as many, say, 2-mana versions of a creature (or spell) as you want. The second, Rush, lets minions attack when they're played, but not players. It's a weaker version of the Charge mechanic, but this set introduces some synergy to get those cards in your hand. There are also new Worgen creatures that swap their attack and health each turn they're in your hand. Lastly, keep a lookout for strategy-defining legendary cards like 'Baku the Mooneater,' which upgrades your hero power if you only include odd-cost cards in your deck.
As the Hearthstone team promised when they introduced the set, Witchwood will also add another free single-player mode: Monster Hunt. Much like the Dungeon Run that came in the previous expansion Kobolds and Catacombs, this new player-versus-computer adventure lets users add cards to their deck as they defeat colorful bosses. And that's it! Go forth and play, card nerds.