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As said above, the last tournament (XCAPS19) allowed technically illegal decks and in-match spec counterpicks, and two tournaments before that (XCAFS18) some of the stronger decks were banned, so the meta’s been a bit different recently. The easiest thing to do is to go to the thread for XCAFS18 and see what was banned and why.
In addition to those bans, it’s common to take a monocolour deck and swap a spec out for Finesse. Using the Neutral starter avoids any multicolour cost penalties, River’s spells are pretty efficient, and Nimble Fencers are good in pretty much any deck.