system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars Legends] What if Darth Plagueis had trained Anakin Skywalker?
gpt
Much the same to a certain point, I'd imagine. If it's Plagueis training Anakin, then Palpatine has been disposed of. Palpatine has either failed to defeat Plagueis, or Plagueis has engineered a situation where Anakin defeats Palpatine, and succeeds him as Plagueis' apprentice.

Plagueis would have manipulated his way to being Supreme Chancellor, initiated the Clone Wars (maybe behind schedule at this point, as he wont become Supreme Chancellor overnight) and ultimately manipulated the Galaxy into declaring him Emperor, and establishing the Galactic Empire - because Palpatine's vision for the new order was shared by Plagueis up to that point. 

His apprentice Darth 'Insert Sith Moniker Here', formally Anakin Skywalker, would probably have had much the same role he had as Palpatine's apprentice, except he probably wouldn't have been maimed by Obi-Wan, so wouldn't be half-cyborg. Obi-Wan would probably have been defeated by Anakin, as Anakin would have been more powerful under Plagueis...

Unlike Palpatine, Plagueis wouldn't have feared Anakin's power, but would have embraced it - arrogantly believeing that no matter how strong Anakin got, he could never defeat the "immortal" Darth Plagueis. He wouldn't have had to worry about Anakin resenting him for the death of Padme, or for turning him into the half-cyborg "Vader". Speaking of Padme, maybe Plagueis actually saves her, he had the power to! Maybe witnessing Plagueis' power over life and death causes Anakin to join him willingly, seeing that no Jedi could be this powerful, no Jedi could have saved Padme.

The infant Luke and Leia are raised as Sith by Anakin, the three of them become powerful beyond all measure (if you've played the latest SWTOR expansion - think Valkorion & his children, same kinda deal) and eventually usurp Plagueis. Game over for the Jedi, the light side in general and for democracy and a free galaxy - checkmate.