Well in theory He could summon any creature. But they would fall under the category of 'summoned beings' meaning that they wouldn't be real. Minotaurs, Dragons, perhaps even humans. But he can keep a summon for as long as he want too. But only a limited amount of creatures and objects at the same time. 


And for the dream he shows them only a Dreamlike perception of reality... like a normal dream that you can't really escape from easily. 

But yeah I'll edit