This deck is just a spin-off of the mono-blue tempo deck that is popular. I' ve actually been doing pretty well with it.
The idea is to add thief of sanity and nightveil predator to the mono-blue deck. Since the djinns are reliant on basic islands, they become a non-bo, but the predators are pretty good finishers and good obsession targets because of hexproof. Mana is jankier than the mono-blue version and I'm still missing a drowned catacomb, but so far so good.

4 Curious Obsession (RIX) 35
11 Island (RIX) 193
4 Mist-Cloaked Herald (M19) 310
3 Dive Down (XLN) 53
4 Siren Stormtamer (XLN) 79
4 Opt (DAR) 60
1 Spell Pierce (XLN) 81
4 Chart a Course (XLN) 48
4 Merfolk Trickster (DAR) 56
2 Nightveil Sprite (GRN) 48
4 Wizard's Retort (DAR) 75
2 Thief of Sanity (GRN) 205
2 Nightveil Predator (GRN) 191
3 Drowned Catacomb (XLN) 253
4 Watery Grave (GRN) 259
3 Dimir Guildgate (GRN) 245
1 Blink of an Eye (DAR) 46

ANy suggestions/ideas?

Well, going UB opens the option of the 4cmc flash siren, kitesail freebooter and other pirate-matters spells and real removal.

Thief should be 4 of as that's you best weapon.

I only have 3 and I cut 1, but I was thinking of putting it back in for sure.

In a best-of-1 scenario, black mana usually means removal, so the threat of it when you don't actually run any is a tool for this deck.
Freebooters are a valid option though, I'll try them out.

I've updated the list:

4 Curious Obsession (RIX) 35
10 Island (RIX) 193
4 Mist-Cloaked Herald (M19) 310
3 Dive Down (XLN) 53
4 Siren Stormtamer (XLN) 79
1 Spell Pierce (XLN) 81
3 Chart a Course (XLN) 48
4 Merfolk Trickster (DAR) 56
4 Wizard's Retort (DAR) 75
3 Thief of Sanity (GRN) 205
2 Nightveil Predator (GRN) 191
3 Drowned Catacomb (XLN) 253
4 Watery Grave (GRN) 259
3 Dimir Guildgate (GRN) 245
4 Blink of an Eye (DAR) 46
2 Kitesail Freebooter (XLN) 110
1 Disdainful Stroke (GRN) 37
1 Sinister Sabotage (GRN) 54

And the deck has been pretty damn good so far. 13-4 (100% winrate since the changes - 4-0). Freebooters have been pretty awesome, not only forcing out removal, but giving you information on what opponent is holding. The good thing about the dimir version versus the mono-blue is that your not so reliant on the obsessions. Thief of sanity is a blow-out card all by itself if you can protect it long enough.
Trickster is still an MVP.
I realized that I needed some extra counterspells to keep the nasty stuff at bay so I'm trying out disdainful stroke plus a single sabotage. So far it's payed off.

with pirates like Kitesail Freebooter, Warkite Marauder, Siren Stormtamer and Dreamcaller Siren in place of the standard Sleep, play Lookout's Dispersal. At 2 CMC it's much better than Spell Pierce.

On top with the pirates you can play Siren's Ruse, which sometimes will be better than Dive Down.