How to obtain and use the hidden weapon "Water Gun"

Unlocking conditions
The unlocking condition for the water gun is to complete the training within 17 seconds in the second half of the tutorial mode (the timed part).

After passing those conditions, the water gun will appear in the upper left corner of the armory.

Suggestions for quickly passing the tutorial level

Switch your weapon the shotgun!!!
The starting guns you have will be at level one the lowest level so you should wait until they are at least level 4 or max level 5 for the reload speed alone is worth the rush through.


The enemy deployment in the training level is:
Level start → 5 robots → sandbags (rolling training) → single robot → small platform (falling training) → 4+1 robots (the last one will fall from the sky after the first 4 are destroyed) → end

Get close to each bot that you can one the training starts and just shoot them in one shotgun blast, then hurry to dodge the swinging bag, take the bot down off the stairs, drop down through the platform and shoot the next 4 bots and the last one will drop from the ceiling!

You have to be fast, not miss any shots and try to keep your ammo up so you always have a shot ready to go! Finally if your on those last 4 bots you can hurry to the finish line seeing the last bot will drop close enough to point blank him and with you already over the finish line it will count!

Instructions
The number of bullets in the water gun is 100, but this value actually refers to the air pressure of the water gun. After exceeding 100, you can still continue to pump air, and the actual upper limit is 999.
When the air pressure exceeds 100, a flashing over pressure prompt will appear in the status bar in the lower left corner, indicating that shooting at this time may explode, causing damage to yourself and forcing the air pressure to drop to 10.

The power of the water gun will increase with the increase of air pressure. It is estimated that the power of a single shot is slightly less than one-tenth of the air pressure. At the same time, the higher the air pressure, the straighter the trajectory will be.