Can someone tell me how to improve my deck please ! and recommend cards to me :P also how do u get marshmellow?

Well if you're going for a dragon deck throw those red eyes cards in there and get a lord of d and flute of summoning dragon. Tyrant Dragon and Felgrand Dragon might help too. Mystik Wok is a good magic card. Also Blue Eyes is still a good monster to use. Blast sphere helps a lot too.