Thank you for your answers!
@Beldin
The low protection of my mage is definitively a big weakness in this deck. I just added Leather Boots and Leather Gloves so that I have 5 armor in total. In general I think I played the deck too offensively. I guess it would be better if I cast the Levi on turn 3 and get out some armor + the ring + a mana crystal (beacuse I often had mana problems) in turn 1 and 2. I don't worry about Eagleclaw Boots too much because I have 3 dissolves to deal with this kind of equipment. I also added a wall of bones because it helps in a lot of situations especially against ranged builds.
I think Banish is a problem for every deck that focuses mainly on one big creature. If my Levi should get banished I just try to keep my opponent at distance, get more armor out and maybe summon a few small creatures that can protect me e.g. by guarding. I can also prevent some of the enemy creatures from attacking me with Lullaby, chant of rage, walls and tanglevines.
@Borg
I already have Arcane Ward in my deck and played it exactly as you suggested it
I like the ideas of enchantment transfusion and shift enchantment so I put some copies of them in.
All in all I made the following changes to my book:
+ 1x Leather Boots
+ 1x Leather Gloves
+ 1x Wall of Bones
+ 1x Mana Crystal
+ 1x Enchantment Transfusion
+ 2x Shift Enchantment
+ 1x Shoalsdeep Tidecaller
- 1x Surging Wave
- 1x Chant of Rage
- 1x Falcon Precision
- 1x Minor Heal
- 1x Water Elemental
I cut the Water Elemental mainly beacause of the spellbook points and due to the fact that there were very few situations in which I had enough mana to summon him. I think more of the smaller creatures are the better choice here.