I agree with everything's that's been said about the Summoning Circle. It is pretty much a Teleport, with the added bonuses that you don't need to account for LoS (or range, for that matter), and is possibly multiple uses. As a 'spawnpoint' of sorts, it also bypasses Zone Exclusive limitations, which could allow you to cast creatures directly in an opponent's spawnpoint zone (or other troublesome conjuration). I also like the fact that as long as it isn't revealed, the opponent has to figure if it is a trap, decoy, sacred ground, fortified position, arcane ward, etc. (?) I love enchantment mindgames.
As a 'main' strategy, I cannot say I've found it very useful so far. Having Fellella cast it could be useful, but as was said, Druid has a better way to cast creatures from a distance, and the Beastmasters have a very powerful spawnpoint already. I'd love to make the card work, but I'm really not sure how.
I thought long and hard about including Hugginn in this book. I love the little birdie, but it is hard to protect him. It often requires at least two enchantments, which increase his cost a lot. I personnally love pushing crows into arena walls, it's dirt cheap and efficient. And leaving him in the center zones generally allows the enemy to Flameblast / Arc Lightning him. I may give him a try though, with a Blur on he becomes harder to deal with.
Regarding the Corrosive Orchid, I just can't help myself, I include it in so many books just because the ability to dodge a Nullify to get rid of an annoying equipment is so good. Also, Unavoidable ranged attack with a chance of corrode is pretty cool. And stacking actions, of course. Fits in with the Wizard's Tower, the same way Ballista + Tower Wizards are pretty disgusting.