Originally posted by Lil brekky:

I believe mountain spawns scale with altitude. So the higher up you go, the better odds of mobs and ore? but I might be wrong

I think there is 3 stages to height;
1) base/transition to mountain biome, contains wolves
2) mid-height you find drakes and eggs
3) upper levels contain obsidian, silver and golems
This is IMO but I might be wrong