Demon portal and all other summoning spells are based on leadership, summoning skill and intellect. The problem is that sometimes even a high intellect can't compensate for the leadership a warrior has (even with low intellect) when using this spell.
Black dragons... a bunch of eggs lie in Sheterra and Rehau, on Nameless island you can find a cave where the game usually spawns some black dragons. It's kinda hard to spot, so keep looking. Should be somewhere in the middle of the island, hear one of the tall crypts (too lazy to check it out now...).
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