From Prototype to Product - The Birth of "SENTINEL INVADERS"

The Spinoff: Extracting a slice of "Project IS0L8T3D" into SENTINEL 519: SAGA - GENESIS

As a solo developer, you are constantly juggling ideas. Sometimes, a prototype for a future project feels too good to keep locked away behind a long development cycle.

That is exactly what happened with Project IS0L8T3D (More details on this title at a later date!).

Working Logo for IS0L8T3D Project

I had been working on a prototype for this project, experimenting with space-combat mechanics, new weaponry, and a distinct lack of "lock-on" hand-holding. I wanted to see what a shooter felt like when it truly respected the player's skill.

The result of that specific prototype was fun. It was really fun.

So, rather than making players wait for the full realisation of Project IS0L8T3D, I decided to take this specific slice of gameplay, polish it, and spin it off into SENTINEL 519: SAGA - GENESIS as a free content update.

This allows me to test these mechanics in the wild while giving existing players a brand new mode to play.

Enter: SENTINEL INVADERS.

Feature Spotlight: The "Hydro-Cannon" Physics

For this new mode, I didn't want standard sci-fi weapons. "Laser go pew-pew" is fine (though this still does exist!), but I wanted something grounded in (pseudo) reality.

I asked myself: What happens to water in a vacuum?

The answer is violent and beautiful. It boils instantly due to the lack of pressure, which causes rapid evaporative cooling, snapping the remaining liquid into solid ice.

The Result: The Hydro-Cannon

Video: Hydro-Cannon in action from older build

In the new mini-game, this weapon ejects high-velocity liquid that flash-freezes into jagged ice shrapnel the moment it leaves the suit.

• Design Note: I’m taking some "creative liberties" with the thermodynamics here (Rule of Cool > Exact Simulation), but the result is a weapon that feels heavy, kinetic, and distinct from your standard plasma blasters.

The Invisible Work: UI Iteration

While the ice physics are the "flashy" part of the update, the real work happens in the UI.

I bridged the gap between Version 191 (Live Production) and the latest version. This gap is filled with hundreds of minute changes that players feel but rarely see.

One major issue in testing was Weapon Anxiety. Players would pick up a power-up but have no idea when it would run out.

The Fix: A Visual Decay Timer

Video: Older iteration of the decay timer

By adding a yellow bar in the HUD that drains in real-time, we communicate urgency without cluttering the screen with numbers. It allows you to plan your attack: "I have 2 seconds of Hydro-Cannon left, make them count."

What's Next?

The SENTINEL INVADERS update is ready to launch in 3 days! (Currently, only on Google Play)

• Logic: Wave spawning and Boss Fight is complete.
• UI: HUD and Menus are polished.
• Next: Let players get their hands on it and tweak based on feedback!

This update will be 100% Free for all existing owners of SENTINEL 519.

If you haven't picked up the game yet, you can grab the premium offline experience right now and be ready when the update drops.

Google Play: 

https://play.google.com/store/apps/details?id=com.AppyBearStudio.SENTINEL519

Thanks for following the journey. 

The sprint uphill continues! 🐻

* SENTINEL INVADERS update is currently only available for Android. iOS (TBD)