11/14/2021 - Small ways to help:
1. If you find yourself falling into the Underworld dimension right after choosing a starter after creating a new game, it's because the game is still loading things and that's causing the "fall onto bedrock to get into the Underworld" part of the Wizardry mod to lag a bit, and think you're falling from further than you actually are. To fix this, type "/tpj 0" to get back to the initial bedrock spawning platform. From there, type "/island create" to generate a tree like normal.
2. Have not been able to successfully prevent Pixelmon raid dens from spawning in dimensions 0, 1, -1, and 413 (void overworld, end, nether, and custom overworld). So, the only way I know to get rid of them is to go into creative mode, give yourself the item "Max Raid Den Spawner", and attack the den with it in hand. Cheaty, obviously, but until I can successfully prevent them from spawning, this is how to remove them. Not really a bad idea to allow cheats anyway, in order to fix glitches that could occur.
4/26/2020 - In addition to an update, I've also created a Discord server for this modpack, feel free to join and ask questions and such. I'm more often there than on Twitch, so I'm more likely to see your questions and comments in a timely manner: https://discord.gg/uyQP34p
Best of Both Worlds is a modpack inspired by the idea that just because you began a game in a skyblock mode, or in a normally generated world, it doesn't mean you have to stay there. The pack contains a large variety of mods, from the magical disciplines of Blood Magic and Astral Sorcery, to varied quality of life and resource production mods, to high tech things like Galacticraft and Flux Networks, and beyond.
While there is a "quest guide" in the modpack designed to help you get started with each mod you want to explore (made with a book and a stick, that's all!), below is a brief guide to actually getting into a position to make the magic happen in a void world, which is the default state:
(Using the Void Island Control mod, default world generation will spawn you on a small platform of bedrock. Typing "/island create" will bring you to a location with 9 blocks of dirt and a single tree. In multiplayer, "/island invite (player name)" and "/island join (player name)" are used to gather your party in one spot. For those who have never played a skyblock map, from there you create the rest of the dimension's contents from that one tree, in this case by using mechanics from Ex Nihilo Creatio: wooden barrels to turn saplings and leaves into dirt, sieves and meshes to sift the dirt into stone, crucibles to turn stone into lava, etc. Use of the item search function added to your inventory screen by JEI is highly recommended.
With your floating base secure, you can create a portal frame out of coal blocks to create a portal to the overworld, like you would use obsidian to go to the nether. Instead of flint and steel to turn the portal on, however, you'll need a diamond hoe. The reasoning is two-fold: first, it requires you to learn enough about skyblock resource generation to get two diamonds, which will aid you if you decide to remain in the void. Secondly, I just enjoy the old joke about wasting diamonds on a hoe.)
If you decide to start in one of Minecraft's other world generation types, or a Biomes O'Plenty world, the portal will just direct you to an alternate dimension. Basically, it works the same by adding another overworld.
If you want to vacate your current world and have a void dimension to call your own, the mod Simple Void World has you covered.
The design philosophy was to add interesting mods that cater to a wide variety of interests. Several mods may do similar things, and which one you choose to use is entirely your preference. Do you use chickens, bees, or mystical agriculture? Accelerate crop growth with phytogenic insulators, cloches, or by breeding crops through AgriCraft? Some combination of them? Your choice.
A final note: there are around 380 mods in this pack, so allocate at least 10gb of memory to your game, through Twitch's options or a command line, and be prepared for a lengthy load time.