Re-Logic's Terraria has been back in the spotlight following the release of Update 1.4, Journey's End, to celebrate the sandbox game's ninth anniversary. However long-time fans of the game might remember a spin-off title called Terraria: Otherworld announced back in 2015. Those who want to get their hands on another game like this, unfortunately, shouldn't hold their breath.
Terraria: Otherworld was first unveiled through a teaser trailer posted to Re-Logic's YouTube account in February 2015, and later elaborated on through an official trailer at the 2015 Game Developers Conference (GDC). According to a forum post by Re-Logic and the spin-off's then-developers Engine Software, it was a game set in an alternate dimension within the Terraria universe that tasked a band of survivors with thwarting a malevolent, nature-corrupting force with deeper role-playing and strategy elements like skill trees and special Purifying Towers.
Though that forum post said it wanted to get Terraria: Otherworld out to the public in 2015, a second post uploaded in 2018 officially announced the termination of its development. It said "we have to be honest with ourselves and realize that Otherworld simply is never going to reach its potential in any sort of reasonable time or fashion." The Terraria developers also said they learned lessons about outsourcing development and making announcements too early, but that some of its ideas "will absolutely yield dividends for everyone."
Some of those ideas may be seen in certain elements introduced by the Terraria Journey's End update. For instance, though there's no official announcement on a connection between the two, the teleportation Pylons in Terraria 1.4 are somewhat visually similar to the constructible towers from Otherworld.
The last major update for the sidescrolling construction and combat game has added tons of new content to give long-time fans and newcomers alike reason to play Terraria now that it's essentially in its finished form. One particularly interesting addition is Journey Mode, which acts similarly to Minecraft's creative mode.
Although Terraria: Otherworld would have probably been an interesting experience, its cancellation likely gave Re-Logic more time to focus on its main game and make that as great as possible. There are also plenty of games similar to Terraria which can give fans more to do if they have time to kill.
Terraria is available now on PC, PS4, Switch, Xbox One, and various legacy devices.
Sources: Terraria: Otherworld Teaser, GDC 2015 Forum Post, Terraria: Otherworld Cancellation