My deck has about 16 clouds. Is that good enough to beat the Riku after..

You would do a lot of damage to him but I don't think you'd be able to beat him with just cloud cards. Riku is annoying but isn't that hard. You should use a normal deck with a few summons, an item, healing magic and lots of attack cards(about 1-3 of them level 0's at the back of your deck). Just hit him with all your attack cards and summons.

Dodge roll to neutralise the dark firaga and use 0 cards when he uses dark aura. A good tactic is to have at least one 0 card at almost all times. Before attacking him head on it's a good idea to fill your restock gague high so you don't have to wait long when restocking while being pummelled by dark aura.

Useful enemy cards are the vexen card, shadow card, air soldier card and the gargoyle card.

16 cloud cards?!?!?!?!?

That's insane! I don't reccomend even 1 cloud card! He takes a very long time to attack, giving Riku plenty of time to break it. I think it's better if you have normal attack cards.

I recommend 9, 8, and 7 cards, and I know there's a sleight kinda like dark aura but I forget it right now ( it lets you fly across the screen like Ariel cept if you keep pressing a you get six hits!) Also, have a lot of zero cards, like one every 6 or 9 normal cards. And have a tink sleight and curaga with high cards too if you get hit by dark aura. It's all really luck, so pray that you have it.