How I would do it.
Season 1 Eden Prime(Bro and Femshep are present) - Citadel (Wrex, Garrus)- Feros/ Noveria/ Liara all at once - Virimire( subvert expectations and kill off a Shepard in stead of a support character)
Season 2 cerberus Shenigans - Illos - Citadel - Collector introduction and Shepard's Death
Spin Off Series - Omega - Shepard's funeral -Team Breaks up - cerberus makes a deal with Liara - Garrus becomes Archangel on Omega and nearly killed - Liara gets Shepard's body back from the Shadow Broker - Illusive man speaks but not seen throughout the series to build anticipation.
Season 3 - Illusive Man opens the season - Shepard is brought back to life - Freedom's Progress - Citadel (Kasumi and heist(Because who doesn't love a good heist episode)) Omega (Garrus - Jack - Mordin ) - Jack and Miranda nearly kill each other - Horizon and Harbinger( ASquad mate dies(Jack, or/and Kasumi)
Season 4 - Lots of Illum(Thane and Samara) - Kill Morinth/Find Thane/ Help Lawson/ Do Liara hacking subplot all on Illum - Shadow Broker got the location of Derelict Reaper - Collector Ship (More squad deaths) - Illusive Man And Shepard have a war of words
Animated Series - Overlord
Season 5 - Modrin & Miranda leave for Tuchanka(Genophage stuff) - Distress signal on haestrom(Tali). Cool ass planet - Migrant Fleet finds Derelict Reaper(Find a nice way to merge all their shyt together) - Harbinger crashes the party with his Heretic Geth - team converge at Omega- Enter Omega 4 Relay
Season 6 - Sucide Run - Lots of Suicide Run - Some peeps dies(Half the crew from being kidnapped) - They try to fix the terrible Human Reaper plot thing... Or just make it floating head with squid like arms(I guess like the machines from Matrix) - Destory Reaper and Collector base - Shepard and ILLUSIVE Man break up for good - Funeral - Shepard is welcome back to Alliance, but it's short lived - Edi decrypt Collector data about Alpha Relay - Arrival - Harbinger says mean things to Shepard and reveals Broshepard has been revived with Reaper tech (BREAPERShep?) and is a slave - Shepard breaks Mass Relay and kill at lot of Batarians *Crickets* Yeah I know - Shepard is arrested
Spin Off Series - Omega Season 2- Shepard court Marshall... Probably the only time anyone pretends to cares about Batarians but still get acquitted -Team Breaks up again - cerberus collect Reaper remains - cerberus takes over Omega - Liara and Legion finds a Leviathan to explain why you make these giant a$$holes(Hopefully they completely rewrite this mess, Idk... Reaper go from galaxy to galaxy harvesting for immortality or some shyt.) Maybe introduce the crucible or something totally less McGuffin-ish
Season 7 - Mass effect 3( Either toss that shyt in the dumpster and completely rewrite it or we continue this disaster)... Reapers tired Of Shepard shyt decides to attack Earth 1st after a quick pitstop at the Batarians crib because nobody like them a$$holes - Go To Mars - Give Edi a body that seems logically porptional. How are we supposed to take her in the field with that dump truck... Absurd - Collect McGuffin blueprint with no idea what to do with it - Go to Citadel for a beer and "This is Fine" vibe - Cerberus fukkery with no existence of Kai Leng - a living Prothen pod on Eden Prime that could make sense of the McGuffin blueprint - Reapers and cerberus converge onto Eden Prime - Revive Javik and he knows fukk all about the McGuffin - Turrian Homeworld gets invaded by Reapers. Krogan laughs. Reaper invade Tuchanka, but it's realize they in the ghetto and bailed but left one Land Reaper.
Season 8 - Just put the Genophage Cure and Geth War here and let it the best damn season of the series. Galaxy United. Then, begin the downfall to an underwelm series ending
Spin Off - Omega Season 3 - Aria, Jacob, and Miranda take down cerberus's Omega stronghold. Jacob becomes a better man LIKE HE SHOULD and gets back with Miranda. If someone dies here... I'm sorry. I live off your ugly tears.
Season 9 - ALL THE Ls, man. Fall of Pavalin and illum. Multiple homeworld being harvested. Losing the battle for Thessia and the Prothen beacon... bREAPERshep vs. Femshep in the Prothen museum. It's a DRAW. A couple of Squad mates are dead. Javik & Liara got the info he needed for the Mcguffin before it was destroyed. They start building Mcguffin super weapon... Javik says they need a Reaper core for device which is conveniently at cerberus HQ. Have a final verbal confrontation with Illusive Man. He's indoctrinated and he off himself and his whole cerberus force as well. Super graphic. Get that shyt and end the season with the galaxy on its last leg and attempt one final all out assault to beat the Reapers. Harbinger calls back about 75% of his peeps to his primary hatefest on Earth.
Season 10 - Well... I guess you can see what happens. Priority Earth. Space and land battles galore.Don't ask me how to do it, because I ain't got the mental capacity for it. Destroy Space Reaper, Land Reaper, and Sea Reapers? I GUESS THEY JUST GIANT SEAHORSE IDK ...
Use Super Weapon to Kill the Reapers, but there is a catch.You only have one shot with this ridiculous super weapon. Cliché builds suspense. So, the critical plot urgency is that Harbinger has a Reaper wall protecting him. Why does Harbinger matter, right? Like a strong vocal presence that's been the mouth piece for the main antagonist should obviously be the main prescence in the climatic ending... Right Bioware?
So, Harbinger has a one way signal to his army. The Super weapon acts in two phases... Dark energy radiation pulse with Prothen/Asari virus that sends a kill signal to all Reapers connected to Harbinger. Hitting any regular Reaper with the Super weapon will only kill the singular Reaper. So, you gotta shot Harbinger while alive with whatever space magic beam. Then, it will cause to send a death signal to all Reapers that overloads their cores and kill them all. So, Shepard got to get it done from land. Hijack a Reaper. Yes... I said hijack a Reaper. Cause complete Chaos. Give Super Weapon open shot. Boom. Probably kill ReaperShep in like some weird ass final boss battle, but it's all sad and tragic because... *Family*.Everyone dies because honestly... I prefer we don't leave open to a terrible sequel series. We have a Citadel (Heaven epilogue) reunion episode.
Characters cut from series : Ashley, Kaiden, Grunt, James, Zaeed
Survivor : Wrex, Edi, Joker, Jenkins BABY