This is intriguing... I can't wait for more.

So...the picture idea is SO COOL. With the different images coming to life and all that. If I were you, I would make this prologue more focused on that idea entirely. Exploring it more would make this super intriguing.

Now, for a few critiques. My main complaint would be that description at times seems excessive. There are some grammar and punctuation mistakes as well, although I don't know if you're looking to improve upon this in that way just yet or work on fleshing out the ideas first.

I'm going to dissect this paragraph-by-paragraph, if that's okay. :)

I stand at the edge of a large window, looking out upon an ocean, cool grey waves lapping against a grey sand shore.

Okay, so with this, I feel like that last part needs to be a second sentence entirely. Also, I'd split up your adjectives in a bit to make it smoother to read. So along the lines of this: I stand at the edge of a large window, looking out upon a cool grey ocean. Waves lap against a (insert adjective here, if desired) sand shore.

Making their way towards the water, large monstrous creatures greyish blue and algae green, slowly walk into the shallows. As soon they touch the water, it turns thick in consistency, no longer liquid.

I like the picture this paints--it's all very creepy and I like that. Especially the bit about the water thickening where they walk. My only critique would be the first sentence. Are they walking out of the water, or into it? If it's into, I would change towards to "into". If it's out, then I'd change it to "out".

The monsters walk on the waters, as if walking on a grey carpet. I watch with dismay, the air around me tainted with the smell of blood and dust. Beside me, stand four others, watching the scene with worried eyes and thoughtful expressions.

I would change the metaphor "grey carpet." I feel like that doesn't do the image justice, plus it uses the word "grey" again, which perhaps isn't the best choice. So perhaps: I watch with dismay as the monsters walk on the waters. The air around me is tainted with the smell of blood and dust." Or you could do showing vs telling, to make this less narrative, perhaps. "I inhale and smell (rust/something metallic)" to account for blood. And I'd take away thoughtful expressions on that last one entirely. I really like 'worried eyes."

I stand there, frozen to the spot, watching, and then everything goes black.

Since you've already said watching twice in the paragraph before, I'd take that away. I stand there, frozen to the spot. And then everything goes black.

Tall, thin and colorful pictures stand, lining a black road which twists and turns out of sight. The tall colorful pictures, standing erect, move with life. Images of homes, dinner tables, livingrooms, and families smiling and laughing together, welcoming and warm.

I feel like the first sentence has too many adjectives to describe the pictures, especially since it's a starting sentence. It needs to have some more oomph to it. I would go with something shorter. Tall pictures line a black road. They're colorful, thin. The road twists and turns out of sight. Then perhaps, to make it more abrupt: Suddenly, the images move with life. (I used images to replace pictures). To account for the images in the next sentence, maybe something like this: They flicker with homes, dinner tables, living rooms, families smiling and laughing together--things welcoming and warm. I don't know if you see a difference in that, but I think it would be more cohesive.

A figure appears, walking on the black road towards me. It is a woman, plump, wrinkled with bright white hair twisted into a bun on the top of her head. She neither smiles or frowns at the sight of me, only nods. She stops to stand before me and puts her wrinkled hands on her round hips, she nods at me, as if in approval.

I wouldn't use "towards" again here, if I were you. Maybe: A figure appears. Drawing near, I see that it is a woman; plump, wrinkled with bright white hair twister into a bun on the top of hr head. The next sentence is fine, although since you use nods in the next sentence I'd remove that. As for the next sentence, it needs different punctuation. The comma after "hips" doesn't work because you go into the next sentence without a gateway. So perhaps this instead: She neither smiles or frowns at the sight of me. Coming to a stand right before me, she puts her wrinkled hands on her round hips, nodding as if in approval.

“You’re here.”
I nod, “I’m here.”
Beside me I realize stands two others, two of the four which stood watching the water turn to pudding. They also nod, and I feel the comfort of having friends by my side. We walk out upon the dark path, which winds through the standing pictures, as a road would through a neighborhood. We pass many pictures in silence, glancing with wide eyes the beautiful images on either side.

I would get rid of the "I nod" completely. And then: I realize two others wait beside me (wait to avoid using "stand" again). And then maybe to avoid using the word "two" again: (double dash from last sentence)--I recognize them from the four that watched the monsters with me. Again, I would get rid of the "they also nod" and go straight into "I feel the comfort of having friends near by. So the whole thing will look like this:

"You're here."
"I'm here."
I realize two others wait beside me--I recognize them from the four that watched the monster with me. I feel the comfort of having friends near by, and we begin walking.

I would, from there, go straight into the picture part. We pass many pictures in silence, glancing with wide eyes at the beautiful images on either side. They cut down the street as a road would through a neighborhood.

Up ahead, the pictures abruptly end, and the black road trails on towards a large, looming forest, dark green pine trees, their height unmeasurably tall.
A faint light shines deep within the forest, and I watch as it gets brighter and brighter. With a burst of light, flame and pine needles, the light breaks free of the forest, speeding towards me.

I really like that first sentence. My only critique would be to edit it a bit this way: Up ahead, the pictures abruptly end, and the black road trails on towards a large looking forest, full with dark green pine trees. Their height is unmeasurably tall. The next sentence is fine, but the following one would read easier and be less repetitive if it was like this: With a burst of flame and pine needles, the light breaks free of the forest, speeding toward me.

I see the image of a large beautiful bird, aglow with flaming feathers, right in front of me.
Sudden pain, a burning sensation in my head, and then… darkness.

I'm trying to figure out how to word this so it uses less words you've already said.

I see the image of a beautiful bird, aglow with fiery feathers. And then space down, and then your last sentence is great.

*takes deep breath* Well....hahaha! :D I'm excited for your story! Keep posting. And I hope this helped.

This is great! I love the imagery, and it's probably your main strength. Looking forward to more!