For some reason, there are actually two places you can get the frog effect. This method is a bit more work than the other method however. Note that in the first room I enter (the bike room), I turn up at the tiles that make a face. This isn't easy to see in the video though, but nonetheless simply walking left a good few steps and then heading up will take you to the door.
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The Frog is an Effect NPC that can be encountered in the Forest World and The Dense Woods B...