As my teacher and friend, Kienan Lafferty of Riot Games, once taught me: 

Good artists copy, great artists steal, and the best artists steal from multiple sources.

Put another way, there is nothing new under the sun.  All our so-called original stories are the same ones that have been told since before the time of Plato.  Anything new and original you think you've come up with, someone else has done before in some form and we're just copying them anyway, so you might as well embrace the fact that we're all thieves and liars.  But if that's the case, from whence comes creativity and why do we not get bored telling the same stories, playing the same games over and over again?  In my opinion, whether it's art, story, film, or game design, you have a fixed number of fundamental elements that go into making the piece, and creativity stems from simply putting those elements together in new and interesting ways, forming combinations and permutations that have never been seen before, even if all the elements in them are ancient and familiar.

A few people have asked what our inspirations were for making Spirit Chain, noting it's not like any other games they've seen.  Suffice to say, we like that.  It means we did our job well. 

To give you a peak behind the current, the original concept stemmed from the theme of the Lost Relic Game Jam: "connection," and our first thought was to make something like Ice Climbers wherein you have one character track the other within a limited range, connected by a tether. You couldn't do certain things without them.  

More specifically, we were thinking of their version in Smash Bros.

Pathing the second character around was too difficult within the time constraint, so we considered how they'd deal with obstacles while keeping close to the main player.  That eventually morphed into being able to phase through walls like a ghost and snapping back to the player, with each character having a different role, different obstacles, and toggling between them to solve puzzles. 

The toggling mechanic was inspired by "Army of Two," wherein one player controls two characters simultaneously who can't progress without the other, although applied to puzzle-platforming rather than combat.

Those of you who've played the game will quickly discover that each character has strengths and weaknesses that must be leveraged to get through the levels and collect all the stars.  The main character can move through talismen (the little banners) but is blocked by spikes while their ghost companion suffers the inverse problem.  We wanted to build on this to have enemies and decals specific to each form as well, but time didn't permit for that.

Originally, we'd wanted to go with more of a Japanese aesthetic, but instead thought it'd be better to focus on gameplay rather than art, so the background elements you see are what we kit-bashed together from packages bought on the Unity Asset Store (and cited in the end credits), lovingly hand-stitched together by yours truly.  A more finished version will see all original assets made from scratch in a unified style.  The characters themselves as well as the ghostly effects were all made by hand, though.

In terms of level design, I take great inspiration from Arin Hanson's video essay on how Megaman uses level design to teach gameplay, as well as his essay on A Link to the Past vs Ocarina of Time, and other channels such as Design Doc and Game Maker's Toolkit.  I highly recommend all of these.  The idea was to avoid verbose text tutorials and use the levels themselves to teach game mechanics, starting with the positioning of the very first lock and key.  As new elements arose, we'd introduce them in a controlled way, such as in Level 2, locking spikes behind gates, giving the player a chance to see them and think about them first, while placing a key there to incentivize trying to grab it (and also making it impossible to do anything else).  This hopefully teaches the player that the ghost can't be hurt but the player can.  Or taunting the player in Level 4 with a star and key strategically placed behind talismen that can't be reached directly, forcing the ghost to go around.

From the start, we wanted to add gamepad support as well, but the aim controls were still buggy by crunchtime, so we decided to scrap it, rather than add in apologies or leave bugs in.  We felt that it would have been a worse feeling for the player to be made aware of what they were missing out on, rather than have a positive experience, feeling everything was complete and intended.

As for the end credits, several people have expressed joy at this being its own interactable level.  The inspiration for this came from the Let's Play community, with several modders, such as Kaze, creating custom romhacks that included interactable end credits.

I know from personal experience, the temptation to just skip out on the end credits, whereas this approach at least rewards the player with sweet, sweet dopamine, keeping them actively engaged instead of just glossing over the creators as if it were a movie they could tune out.  Hopefully, they take the time to look at their surroundings in the process; and since ours is a puzzle game, we added locks and keys to control the pace at which the player progresses, forcing them to stop at several intervals while waiting for the doors to close.  To make this feel less like a chore, however, we added a few stars as a final reward for sticking it out.  You can technically skip them, but we know you won't want to.