This stage wasn't in Smash 4, but it was in Brawl and originated in Melee. During the Gamecube days, it basically upgraded the old N64 stage Dreamland. Obviously this one is from the Kirby series of games with an expanded stage.
Like Dreamland, Whispy Woods can send gusts of wind your way, but it's rather weak.
What to look out for are the blocks. The star blocks are fine, but when you break the others?
Well, let's just say, you'll learn how to fly. Not my favorite stage in the series, but I always had a soft spot in my heart for it.