my Hobbes is a Madcat
Firstly, Joel Eddy was right. This game is magic.
Secondly, I played my first game with my son last night. He tried to summon a demon and rolled a 1, which meant a large one should appear. He empowered the spell to make it a medium one. It immediately attacks, as per the rules, but does it again activate in the creature phase or is it considered to already have been activated?
I've not seen an official ruling on this one, but I would make a case for it activating again in the creature phase. First off in the rules for the creature phase it specifies any "creature not directly under control of a player" rather than "unactivated" creatures.
But more, I think of Frostgrave as "misadventures in magic" and the whole game works to remind you that just because you have he title "wizard", you are not in any way qualified to handle anything more magical than a potato-battery. So all spells hurt when you fail, but some spells are so
powerful dangerous for a novice magician to begin with that they have added penalties when failed. I don't think the intent of having a critical failure rule in the summon spell is just to be a pain... i think its meant to maul your wizard... for the sake of thematic hilarity.