King Kung is a hardcore adventure modpack balanced around Better With Mods. It contains several mods to challenge the player, such as AtomicStryker's Infernal Mobs, Mutated Mobs Mod, and Tough as Nails, as well as several mods that provide many new places to explore, such as Biomes O' Plenty, Glacidus, and The Twilight Forest.
One rather important starting hint: you can't get anything without the proper tools, except for Sticks by breaking Leaves. With Sticks, you'll want to make a Digging Stick and then find Gravel. Then, you can make Stone tools out of Flint.
Lastly, keep in mind this world isn't a friendly one. There's plenty of things that might get you, and I won't be listing them. Just keep your eyes open. It's not easy being king.
For a full mod list, click the "Relations" tab in the upper right corner of the browser. Consider donating to the mod authors; a Patreon list can be found here. This modpack also includes FoamFix by asie.
Note this modpack is currently somewhat WIP.