Mass Effect: Legendary Edition let fans relive the original trilogy with remastered graphics, quality of life changes, and fixes to common fan grievances from the Mako's controls to Tali's face reveal. It also helps re-establish the original Mass Effect trilogy as the core of the franchise before the release of Mass Effect 4, which appears to pick up the story from both Mass Effect 3 and Mass Effect: Andromeda.

This poses a huge task for Mass Effect 4. Although BioWare has hinted that both the original trilogy and Andromeda will have links to the next game, there may have to be some huge developments in the Mass Effect universe to make that happen. Here's all the evidence pointing to the Mass Effect 4's biggest challenges, and some of the ways BioWare may be hoping to make it work.

RELATED: Does This Unit Have A Soul? Legion's 10 Best Quotes In Mass Effect

There are a few key details that fans have already been able to glean from what little has been revealed about Mass Effect 4 so far. For a start, the game's teaser trailer shows fan-favorite companion Liara T'Soni traversing an unknown planet, walking over the huge husk of a dead Reaper, and finding a piece of N7 armor resembling Shepard's.

This immediately suggests continuity with the original trilogy, with the next chapter picking up where Mass Effect 3 left off. More specifically, the dead Reaper suggests that the next Mass Effect will be set at least partially in the Milky Way after Mass Effect 3's Destroy Ending: the only ending which killed the Reapers and had the potential to hint at Shepard's survival with a high enough Effective Military Strength.

This is backed up by an image released by BioWare showing a Mass Relay being rebuilt in the architectural style of the Systems Alliance - it was only the Destroy Ending that saw the Mass Relays destroyed. However, the trailer also opens with a shot of both the Milky Way and the Andromeda galaxies, which BioWare Project Director Michael Gamble has stated is "intentional." Not only that, but a piece of art for the upcoming game shows a silhouette which matches Jaal's from Andromeda, despite Jaal's species only being found in the Andromeda galaxy.

Connecting the events of Andromeda and the original trilogy poses some huge challenges for Mass Effect 4. First, the events of Andromeda take place around 600 years after the end of Mass Effect 3, lightyears away from the original trilogy's setting. There are a few ways the presence of species and characters from Andromeda could be explained, each with their own set of challenges. It is possible, for example, that Mass Effect 4 could be set hundreds of years after the end of the original trilogy.

This would explain how the galactic community has had time to rebuild after the Reaper invasion, and the long lifespan of the Asari would explain why Liara is still alive. She'd be around 700, with many Asari living to be 1000 years old. It is possible that Mass Effect 4 takes place after the Andromeda Initiative was able to set up a working Mass Relay connecting the Milky Way to the Heleus Cluster.

However, this would make explaining Shepard's survival difficult if the game wants to bring back the hero of the original trilogy. Shepard's unique biology after their resurrection might form the basis for an explanation, but a time jump would also likely mean fan-favorite companions like Garrus Vakarian would be dead. Living up to the original Mass Effect companions could be extremely difficult.

Mass Effect 4 could somehow be set shortly after Mass Effect 3 if the Andromeda Initiative has managed to travel backwards through space and time. If so it will be faced with the challenge of explaining how that happened without introducing time travel elements that would disrupt the entire Mass Effect universe. Either way, the inclusion of elements from Andromeda also means Mass Effect 4 will have to address some of Mass Effect: Andromeda's biggest hanging plot-threads.

RELATED: Former Bethesda Developer Joins New Mass Effect Game as Narrative Producer

Mass Effect: Andromeda was packed full of storylines which never got full resolution. The true nature of the Jardaan and their reasons for creating both the Remnants and the Angara remains a mystery. The Andromeda Initiative's mysterious benefactor and the reasons behind Jien Garson's murder also have yet to be revealed. The nature of the Scourge — a mysterious dark energy force found in Andromeda — also leaves Mass Effect 4 with some big questions to answer.

Some of these unresolved plot-points could be the key to connecting the events of Andromeda back to Mass Effect 4, however. The Scourge, for example, was extremely enigmatic in Andromeda, and was known to break many scientific rules believed to be doctrine by the species of the Milky Way. A cut dark energy plotline from Mass Effect 2 would have seen dark energy connected to temporal phenomena, so the Scourge could be key to sending the characters and species from Andromeda back through time and space.

Regardless, Mass Effect 4 will face some ginormous challenges. It will need to play out the consequences of the Destroy Ending, likely including the destruction of sympathetic synthetics like AI characters and the Geth. It will need to explain Shepard's survival if they're returning as the main character. Plotlines from Andromeda will need to be resolved or expanded upon, and though they could help kick off the next game they could equally bog down the plot with storylines originally intended for an entirely separate Andromeda trilogy.

After the release of Mass Effect: Legendary Edition, Mass Effect 4 is also faced with a fanbase holding fond memories of the original trilogy fresh in their minds. That's a huge legacy to live up to, and a high standard Mass Effect: Andromeda already struggled to meet. Mass Effect 4 will have to perform a balancing act between elements from Andromeda and the original trilogy, telling a new story that still acknowledges many of the decisions players made across both parts of the series so far. Mass Effect: Legendary Edition is a reminder of some of BioWare's best work, and many fans will be curious to see if the studio can one-up itself in Mass Effect 4.

Mass Effect 4 is in development.

MORE: Mass Effect: Legendary Edition Update Fixes Major Issue with Xbox Version