Guide to unlocking the Revolver Alternative upgrade.
Revolver Alternative Upgrade
Introduction
You may have come across a stone tablet Button marked "VI" in your travels in 1-4 with a pretty large door behind them.
That door leads to a special upgrade turning that peashooter in a boss killer.
The following guide will show the Buttons for you to find and activate to get that upgrade.
Note: you only need to activate the Buttons once for it to count (with the final Button near the door behind the exception).
Button "I" - Found In Limbo 1-1
The first Button can be found later on in the map in the final room.
Defeat all enemies then destroy the skylight.
In this case, I recommend shotgun-jumping to give you enough momentum, then the Button is right in front of you.
Blasting yourself up in the air will land you on the roof.
The Button is the only thing on the roof, so press it and you've gotten step one.
Button "II" - Found In Limbo 1-2
Process into the level and visit this room before the final battle room.
Turn right and see a destructible wall.
Break that and move on into and process forward, keep note of the room closed under the bridge.
Move forward and find another destructible wall, take that down and move ahead.
Now, I'm actually not spoiling this one for you, continue into this section and enjoy the secret!
After finding the secret, come back out and visit the room that you remember under the bridge.
It's now open and so drop down.
Smash that Button and you're one step closer to getting your hand on the upgrade!
Button "III" - Found In Limbo 1-3
To get this Button, you must collect both Red and Blue skulls and place them on their respective pillars
Turn around and you'll see one of the stained glass descending, head over there and enter the room.
Head up stairs and enter the room above.
Go down the hallway and get ready for a fight!
You'll now need to face down two sword machines at the same time!
The goal is to reduce both swordmachines's health to the lowest at the same time. Take one down and reduce the others to win, otherwise the downed swordmachine will regen health and continue the battle with you.
Clutch it up and the door behind them will open, it's your beloved Button!
Smash it like your favourite YouTuber's subscribe Button!
Button "VI" - Found In Limbo 1-4
The final one is the easier one!
Return to the room in the left of the castle.
Press that final Button and boom, you've done it!
Jump to your prize in joy and claim it!
Enjoy a magnum version of your Revolver, you can now switch at the shop to which version of the revolver you wish to have.
This alternative works on the base revolver and the coin flip version.
Source: https://gameplay.tips/guides/8414-ultrakill.html