This is another old game similar to Marble Blast, called "Marble Sheep", developed by Ulf Ackermann (ackBytes) and released in December 2007.
Gameplay video (in German)
In this game, the protagonist, Utz Wollewutz, enters mean wizard Firlefranz's yard and eats apples from his tree. Firlefranz gets angry and traps Utz in a glass marble. Utz must get to the kind wizard Mumpelwitz to reverse the spell. Here, you control Utz who has to go through 28 levels (not 30 as advertised), collecting apples while avoiding monsters.
I first heard of the game back in 2007 (when I was eight) while surfing the net. For my 12th birthday (in 2011) I bought the full version and beat it in less than a day.
I feel this game had a lot of potential and could have spawned a sequel. Unfortunately, the game is rather hard to come by these days. So far I haven't been able to contact Mr. Ackermann or the publisher (rokapublish) as to what happened with the game. The closest one can get to the full version is a used CD-ROM copy on Amazon Germany for 67 euro cents (~77.53 US cents), but the quantity is very limited (five used and one new as of this writing). The demo is still available in some download sites.