"If you get the book, then you can go through the door in level 11. There, you can find the hammer."
I personally advice you guys to not treat this hint as a reliable source on how The Mask looks like, since the "Хочешь - верь, не хочешь - проверь" section is flooded with gossip cheats which have never been tested by The Great D editorial in the first place. That is, unless the levels are actually divided to sections here, which explains why there are "more than eleven stages" in the game.
EDIT: ...the Mortal Kombat V Pro invincibility cheat seems to be legit, though.
EDIT 2: ...what I totally can't say about the hint for Tom & Jerry (and Tuffy) placed among the regular and tested cheats! Just look at this: "There is no escape from the secret room in level 3, so, without hesitating, die on the ant and you'll be respawned back to the regular stage".
And now, the reality. The levels are divided as X-1, X-2 and X-3, so it's completely unclear which bonus stage the kid have meant exactly - that's one. None of the bonus levels have actually deadly hazards, sans 1-1 and 1-2, not to mention none of these have ants - that's two. And the last fact: all the bonus stages are escapeable.
Geez, what kind of a wussy ass tips 'n cheats section is that?