NCF – Extended list of Neutral creatures.

Hey, can someone explain something to me? I just can't figure it out. So, a Berserk summoned by a hero is 2/2. A Berserk summoned by a Balrog's whip is 2/2. A Berserk summoned by a Dark Dragon is 3/3 (a Berserk summoned by a whip attack is 3/3. If you cast it as a spell from a spellbook, it's 2/2). How does it even manage to be 3/3? All the attack-based summons are like this, and I haven't done anything special, but Warlocks and Balrogs in the same situations create 2/2 units? Oh, it turns out that to get 3/3, you just need to have that specific spell in your spellbook.