18 Island
2 Network Disruptor
4 Faerie Miscreant
4 Faerie Seer
4 Moon-Circuit Hacker
4 Ninja of the Deep Hours
2 Mirrorshell Crab
4 Mantle of Tides
3 Aether Spellbomb
3 Blink of an Eye
2 Make Disappear
4 Disruption Protocol
2 Of One Mind
4 Hieroglyphic Illumination

To be fair, the Pauper Midweek Magic events are not a competitive environment; there are a lot of just-for-fun decks and random stuff thrown together in the hope of squeezing out 3 wins. Still, this deck works great and I'd take it to a tournament if there were any.

Card thoughts:

By the mid-game you can usually cast Of One Mind for one mana, since all the ninjas are humans and the rest of the creatures aren't. It's a great rate, but the card's not essential to how the deck functions, so feel free to replace it with anything.

The Mirrorshell Crabs are probably too cute. In ~40 games I've yet to cast them as creatures, even when I've had enough mana. I'll probably replace them with the other two Make Disappears next time. Still, they do some things other counters can't: the channel ability can counter other abilities, and is difficult to counter itself since it's not a spell. The Crabs might be good in the sideboard if you're playing Bo3.

Other ninja decks I faced seem to like Lantern Bearer in the cheap flyer slots, since its flip side can eventually allow the ninjas themselves to fly. I like the idea too, but I'm running Network Disruptor instead to provide a couple more artifacts for Disruption Protocol, which is a fantastic counterspell. Disruptor's ETB ability isn't amazing but it's definitely relevant sometimes.

Mantle of Tides is incredible in this deck. It lets your X/1s block, it helps you cast Disruption Protocol, and it turns Hieroglyphic Illumination into a combat trick. (You have to pay the full 4 for Illumination on your opponent's turn, but on your own turn, just cycling it is sufficient.) Note that Mantle's trigger isn't optional, but you can have it target the same creature that's already equipped.

No Lonely Sandbar, Mystic Sanctuary, or any other tapped lands for two reasons. First because you absolutely must play untapped lands on your first two turns in order for the deck to get underway. Second because as long as you can keep drawing cards, you can keep spending a lot of mana, even in the late game. You're usually not sad to play your sixth or seventh Island, provided it wasn't the only thing in your hand.

Mulligan decisions: most hands that have two islands, a 1/1 flyer, and any other spell are probably good enough to keep.

This archetype is one of my favorites in actual Pauper, and I'm thrilled that a substantially similar list can be built on Arena.

Would love to see other people's ninja lists, or whatever else you're playing in Historic Pauper.