Underworld: The Shelter is a more deep and personal take on the management simulation formula that was established in Fallout Shelter, and expands on many of the RPG elements that its inspiration mostly just alluded to. The game apes the main plot of Fallout Shelter in a lot of ways, and you'll manage an underground shelter in a side view, but that's about where the similarities end. Many of the mechanics involved in running a successful shelter revolve around expeditions, and that's where things start to get interesting.
Background: The game's tutorial throws you headlong into this big differentiating mechanic. You'll grab a character and head out to some ruins, where you'll find a few treasures that will help you build an infirmary, along with your first mutant, who will become your second resident. In that sentence alone, four mechanics were outlined that differentiate this game from the genre originator and its various clones. These top-down expeditions see your character heading out to irradiated ruins and clearing them out to stop the poisoning before their health runs out. While you hunt for items, money and mutants to rescue, a robot by your side takes automated potshots at enemies. Avoiding said enemies is up to you. You'll also be able to pick up perks and equip items to positively change your exploration experience. When you return, you'll use certain required resources to build new rooms, and you'll be able to stick mutants into infirmary pods to bring them back to normal life. Individual character types and stats play a huge role in what they're best at, how they level up, and what you'll want to use them for. Rather than the extremely customizable training system in Fallout Shelter, residents in Underworld grow organically as they gain experience in the ruins, or through manual level-ups at home that cost coins and have a chance to fail. A high-level wanderer may be worthless in the clinic, while a high-level miner with high strength may have no business outdoors due to their low speed. In order to house efficiently and create a well-oiled machine of an underground society, however, you'll have to do one thing you never had to do in Fallout Shelter and similar games; be cruel. Not every mutant has the potential to become a worthwhile addition to your shelter. You can see their human stats before you turn them. Those that won't be worth the resources and space can be banished to the wastes from whence they came, and you'll actually have to do this in order to avoid filling up your shelter with low-potential residents that won't facilitate expansion and the overall health of the population. This mechanic becomes extremely important in PvP, where you can raid other shelters, and of course be raided, for residents and resources. Having a suboptimal team can spell disaster in battle, and lead to irreparable damage to your operations.
Impact: This is a quirky, unique, and low-profile indie game, so you can't really expect much in terms of lasting impact on the Android gaming scene. One thing it does seem set to accomplish, however, is showing that "Fallout Shelter clone" can be a real genre, with enough variation and differentiating game mechanics slapped on. Hopefully, this bold decision will cause the game to become popular enough to spark up a trend and we'll begin seeing more and more games ape Fallout Shelter's delightful core mechanic with increasingly creative twists.