I'd take out 2x Marshmellon and add 2x Tour Guide. This way you can have Acid Golem as your own beater and can Swap it afterwards. 1x Zenmaines instead of one of the Blackship of Corn if you do this.
I would also take out Samurai of the Ice Barrier and the two Gishki Avances for 3x Gishki Abyss. Abyss is much faster than either and finds a Gishki monster for you right then and there. It is yet another target for Creature Swap if you see a monster that can easily get over it (and those will be a lot, it is only 800 attack).
I'm not sure if you even need those Elemental Heroes. If you want to keep them in, definitely add Stratos and atleast one Reinforcement of the Army or E - Emergency Call. I'd run Stratos and 2 E-calls over 1x Mystic Box and the second Samurai of the Ice Barrier.
Shien's Spy isn't that good (you didn't list it by the way). Mystic Box and Creature Swap are already better, and with only 5 targets you don't want more than 4 swap cards. Even if you do the changes I made, you'd have 8 targets with 5 swap cards (without Spy), which is a very good ratio imo. Maybe you could add Summoner Monk since you run so many spells; it'd speed up the deck.
I hope this helps you, definitely try things out and play with ideas.