Memory Sluice is amazing with a couple of Grimoire Thiefs. Scalpelexis is also great.
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Why do you have 29 land? That is way too much!
Lime and the Coconut!
I think need a lot less 'One Of's' If you want to make an assassin deck, you will want more then just one Royal Assassin. Get 4. I would take out ALL of the artifacts except for maybe the Silver Myr and Vault Skirge. If you have a few creatures with life link, you don't need life gain. You just need your creature hate and a few that will attack every turn. Dunerider Outlaw is another great card. Comes out on turn 2 and gets bigger every turn if you can control the field. Another fun combo with the Nettling Imp is to have Wall of Souls out, have the imp force something with power 2-3 to attack and block with wall of souls to deal all the damage back to the opponent. Or to use it to force their huge dude to attack you and kill them self with the damage. Standard assassin decks also involve cards that will force the opponents creatures to tap. Two great cards that do this are Rathi Trapper which forces it to tap, and Nettling Imp, which forces the oponent to attack with the target creature. As they attack, you can tap royal assassin to kill it, or block with something larger. Its great for killing off their weenies. I would also suggest Guul Draz Assassin. He is a great 1 drop and by turn 3 you can be kill off anything 2/2 or making things bigger deal less damage. Midnight Charms are also really useful. As are Sadistic Glee on something you want to have attack every turn like your Vault Skirge or, what I would suggest instead of those, Vampire Nighthawk.
Since you will likely have quite a few merfolk out soon, swap mana leak for spell syphon.