Your chapter discovers an artifact...

Lorgar was always headed in that direction; unless the Emperor worked out how to deal with his (legitimate and Emperor-inflicted) issues in a non-retarded manner (i.e. Monarchia), it was always going to be a matter of time. And if it wasn't Chaos, it'd have been Xenos Archeotech (imagine if he met a C'Tan), or whatever.

He might not have triggered a civil war bigger than one Legion - though if he tacked onto the C'Tan he might have brought most of the mechanicum and maybe the Iron Hands with him - but it was his nature to search for the Primordial Truth, and he would have found it, whatever he decided it was.

In short, stop Magnus first; everything else is a minor detail.

So the way to solve the issue with Magus is father/son bonding time over psychic powers and the nature of the warp?

You wouldn't know how much damage Magnus caused.

The webway was beyond top secret; other than Malcador, maybe half the primarchs had a vague idea about what it was going to be; and the Sisters of Silence and Custodes knew after everything went to shit because they assisted in containing it. But besides that, no-one knew anything about it, before or after.

So if you're from a chapter 10,000 years later, you have no idea about what Magnus triggered.

There's a laundry-list of just about everything that the Emperor and all of the Primarchs did wrong (or at least could have done much, much better) - it's called The Horus Heresy. Some are more retarded than others, but not one of them behaved at all intelligently.

In answer to your question, basically yes: the Emperor doesn't get to be Dad and tell them what to do and at the same time expect them to be as good at handling their superpowers as he is.

If he created them as equals, he should have treated them as such. If not, it was fully his responsibility to keep them supervised. He didn't have to be their dad, but he was undeniably their creator in every sense. If he didn't have the foresight to understand their unique powers and deeper motivations - as deliberately engineered into their composite being as was their flesh and blood - and didn't trust them enough to explain his secret plans and didn't bother to keep an eye on them either, well, no wonder everything's fucked.

>what Magnus triggered
Or even who he is.

My Party is all Dark Angels...

Immediately start hyperventilating while trying to explain in as few words as possible, that I'm from the future and Lorgar needs to be stopped immediately, too fast to be understood while pulling on there arms.

Ask them if they've heard the good news

Emperor tells you that Heresy is actually his plan to test the Humanity for even greater coming danger he saw in empty void of the distant space

>land on a planet with a future traitor legion
>"Once a heretic, always a heretic!"
>Erebus isn't the first heretic anymore

>"heretic" group of space marines discovered
>disputed being similar to a legion, no one is sure how you exist
>E money realizes that chaos must have done this, and realizes how big of s threat they are
>your chapter dies to prevent the heresy

Likely start shooting, if there's no way to know you were transported back in time, you could just think you were TP'd to an other planet

>perturabo posting so soon

Every time

This!

So... his plan is to remove a good half of the best possible defense humanity could have, knock technological progress into an ever downwards spiral, and destroy untold amounts of industry and infrastructure.... why again?

Compare to the alternative future where humanity is moving towards all psykers all the time with perfects superhuman genome, all sons of Big E...
and then Tyranids.

The 'Nids assimilate the Emprah's genetic code, and add in some Ork for good measure.

Humanity is no more. Xenos are no more. Chaos is no more, the Warp is the dominion of the Overmind.
Unless Necrons warp out of the galaxy, the brief spark of sentience is snuffed out of the whole Universe.

Because the BL writers couldn't be arsed to come up with anything better.

^this

Seriously, I'd skip all the BS and go to Prospero and warn the Thousand Sons. Those guys were Bro-Tier pre-heresy and Magnus ruining the Emperor's project was probably the biggest damning piece of the whole thing.

I can't even tell who is fighting who.
Or is that the point?

>be red scorpions marine
time to save our primarch! ...er i mean uh that horus guy that im totally not related to.

and also bro down with Loken for having the biggest space marine dick on the planet

Doesn't look like they're fighting; looks like they're working together to secure and objective of some sort?

I hadn't heard of it, so probably just another piece of Black Library cancer that continues to justify my choice of not reading any into adulthood.

Well, as blood ravens, it really depends on if we know our chapters true history or not.
If we do, then it's simple: find the Corvidae fellowship, tell them about what's going to happen and that they need to get the hell put of dodge, and quick. Don't warn or stop magnus, because that's pointless. If he's stopped then the blood ravens never exist (because then the thousand sons would have stayed loyalists, assumingly), and that both creates a paradox and screws us over, since now we get the mutaded gene seed rather than the purer one of the blood ravens.
If we don't know our chapters history, it's simple, we move onto what we would do after warning the Corvidae fellowship: spend time collecting as much relics and knowledge of the period as possible, trying to keep out of sight and knowledge of anyone for a rather great deal of time. With this knowledge and relics, we will be more prepared amd know what to do when are futureselves are sent back again.

Finally name should be "Heresy grows from stubby arns."

Kill Abaddon and that Death Guard guy, Thyphon or whatever. Those two are probably the most responsible for death in the 40k universe

So my Imperial Fist succesors gets sended to the Dark Angels because they look a lot alike.

First thing first, gasp in awe to see the Imperium in his golden age and once we find our primarch progenitor ask for an autograph. Then probably start working on warning Emps about the Heresy, then ask him for an autograph too like the bloody two meters and half tall fangirls we are.