Starting Info
Skylines is an Expert Styled modpack. An expert pack generally increases the difficulty of some if not all aspects of a playthrough. If I were to give a comparison for pack as a reference point, I would point towards FTB's Infinity Evolved: Expert.

This pack heavily emphasizes automation and resource management. While technically you could progress through this entire pack without doing much of either, you will be rewarded for any automation you do as you progress through the pack. Automation will help you complete all the steps to get the later tier base machine block for each mod, as each mod in the tech path utilizes some components from previous tiers. For example, in order to start into Buildcraft, you must first have progressed into Immersive Engineering and Pnuematicraft. A brief rundown of the tech path can be found on the discord, link found at the bottom.

For this pack, mobs are more dangerous than normal, without going too over the top with new mob types. This has been done through a combination of Rough mobs 2, Primitive mobs, and Zombie Awareness. Most mobs are dangerous or foreboding when you are first starting off, as they can and will swarm you. Some places are never truly safe. Playing on hard... can get pretty brutal.

Origins of the pack
Believe it or not, this pack, or more aptly put the idea of this pack, has been in and out of development since 1.7.10. This pack originally started off as a personal offshoot of Infinity Evolved: Expert (IEE) that added a number of other mods and some small tweaks to the configs/recipes as I deemed fit. Fast forward to 1.10.2 where I attempted to make a combo pack that had magic and technology intermixed with more of a tech tree feeling. I got to around 66% completed before I burned out and dropped minecraft for a while. Fast forward to 1.12.2. This is where the pack was reborn into what it is now. It borrows a number of ideas from other packs, but mixes them together differently. All together, in just the 1.12.2 version I have easily 100+ hours on my current dev play-through and probably about double that in the backend part of the pack (configs, scripts, choosing mods, solving conflicts etc)

Installation Suggestions
I HIGHLY recommend installing optifine. Optifine, at least for me, greatly increased my FPS, and removed some "stutters" due to its more optimized rendering code.
I recommend at 6gb+ of ram dedicated to allow the pack to run well.

General Info
This pack has a few "Immersive" things added to it and key differences from traditional minecraft modpacks, that should be stated prior to your starting.

First, every world starts off in Early Spring, and will slowly rotate through all seasons as each MC day passes.
Second, mobs are generally more intelligent, vicious, new varieties or some combination there of. Getting hurt will attract most nearby mobs, they will investigate light sources and loud noises. Make sure you protect your base with at least a fence!
Third, you have to keep a relatively balanced diet, if you don't you will suffer some penalties, and if you do you will gain some passive buffs.
Fourth, normal torches are locked behind a torch that decays over time (burning torches mod) and glowstone. These decaying torches decrease in light level, and can set potentially nearby blocks on fire, and will damage entities that touch them. Thus it is in your interest to gain access to more permanent light sources!
Fifth, you can chop down an entire tree with an axe by chopping the bottom block (if it is a dynamic tree), or by shift chopping if it is a non-dynamic tree (vanilla/natura etc). The world will initially generate with dynamic trees, and you can convert their seeds to regular saplings with a bucket of dirt and the seed.
Sixth, and possibly the most important, is that resource veins are drastically different from regular minecraft. Instead of relatively common small veins, you have uncommon/rare/extremely rare veins that are exceedingly large. Don't worry, they maintain the same world height range as they would normally. Each resource vein should easily produce a stack of materials/ore, if not much more.

Closing

I hope that those who play through this pack find it enjoyable. if you want to give feedback, make a suggestion, or report any inconsistencies I managed to miss the best place to do so is through my discord channel for Skylines. This discord server will be the primary/fastest means of communicating about the modpack. https://discord.gg/tT9UgVR

Skylines Expert

Actually Additions

Additional Enchanted Miner

Advanced Rocketry

AE2 Stuff

AE2 Wireless Terminal Library

AgriCraft

Alternating Flux

Angel Ring To Bauble

AppleSkin

Applied Energistics 2

AtomicStryker's Infernal Mobs

Avaritia 1.1x

Baubles

BdLib

Better Builder's Wands

Better Foliage

BetterFps

BiblioCraft

Bookshelf

Brandon's Core