If Costume Closet has left the battlefield or has no +1/+1 counters on it by the time its activated ability resolves, you won't put a +1/+1 counter on the target creature
Secret Lair has also been used to introduce cards from other brands, reimagining existing cards with new art, names, and flavor to fit the crossover theme
It can win a prolonged game, but your entire plan is telegraphed and your opponent can adjust accordingly
Plus, you get to make a deal with a deck that can make use of some 0/2 plants, which can buy you some good grace
I see this getting played as a pseudo-wrath in blue decks that dont have access to whatever sweeper we end up with
If a deck can be built to contain mostly or only cards of that type, then the lands have no restriction other than the deckbuilding constraints