The first character i unlocked: The Lost One
The Lost One has about a 10% slower WALK speed than Boris, and a 50% slower walk speed than Sammy, but has a faster sprint.
To get the Lost One, all you need to do is search lockers, dead-boris...es(?), and toilets. When you do this, you have a chance of getting a Lost Page. Once you get enough of these, (i'm not sure how many) you will obtain the Lost One when you arrive at the safehouse.
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Also, some people may be curious about what that ink boris is in the main "kitchen" area in the safehouse. That's the Character Selector. When you unlock a new character, you can go to that inky blob, press E on it, and it will change to the next character in line, in this case, the Lost One.

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So, that concludes the step-by-step tutorial on how to get the Lost One. Onto the star of the show, Sammy.

So, you wanna know how to get Sammy.
Well, it's either really easy or really really hard. I'm not sure if i got lucky, or if it's just really easy.
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Same thing as the lost one, really.
Firstly, you need to collect 4 Candles. You can check your progression on this by going to the Guys Bathroom in the Safehouse. The Candles are found in lockers, dead boris...es(?) and toilets.
Once you get the 4 Candles, you will be assigned a new task once you go back to the Guys Bathroom. You must find Sammy's Mask.
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Now that you have the man himself, let's go over his abilities.
First, Sammy has a 10% faster WALKING speed than Boris. This makes it so that you are the same speed as the Ink Demon.
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Second, the main draw, your sprint. Sammy doesn't have it. As Sammy, you trade the ability to sprint, be able to use "Ink Portals."

Instead of using your bacon soup meter to sprint, you use it to cross through the Ink Portals.
Crossing through an Ink Portal will cost 20% of your stamina meter, giving you 5 "Charges", as i like to call them.
Crossing through an Ink Portal will bring you to another Ink Portal somewhere else in the level.
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So, that's about all that you need to know. If this guide does well, i'll make another one teaching you how to unlock Butcher Gang Encounters and Alice Encounters.

>> BORIS is being used as the baseline here. <<

Boris has an average walkspeed taking about 6 seconds to walk from the Bacon Soup station to the Little Miracle Station in the Safehouse.

The Lost One is the slowest walker in the game, taking 10 seconds to get from the Bac. Soup station to the LMS in the Safehouse.

Sammy is the fastest walker in the game, taking only 5 seconds to get from the Bac. Soup Station to the LMS in the Safehouse.