Below is the post on how to get different units from the Call Colossus scroll using eggs:
http://forum.1cpublishing.eu/showthr...=call+colossus
As for the number of units you get, as the definition states, it depends on your leadership. For example, red dragons require a leadership of 2,000 each. So if you have a leadership score of 6,359 then you could generate 3 red dragons from your Call Colossus scroll. If you happen to have 2,001 leadership then you could only get 1 red dragon from the said scroll. If you have less than 2,000 leadership then you have no chance at all of getting a red dragon from the CC scroll.