The Steel Path

Hard mode enabled!  The Steel Path is basically just that.  Debating if you're ready for this?  Don't fret any further.  Let's see what happens in this new game mode.

In order to access The Steel Path, one must have a completed Star Chart.  If this applies to you, make your way to Teshin and get it unlocked.  Head over to any relay, access the fast travel, click Teshin.  Boom, you're there in his area.  Speak to him and click either option in order to enable The Steel Path.  Once you have done this, congrats!  You can head back to your orbiter and you can see that there is now a new image on the HUD.

Look on the right side

This mode allows you to redo the entire Star Chart (like you did before, node by node, starting on Earth), only the enemies are scaled in level by +100.  When completing the new harder leveled planets, you are awarded new emotes and trophies.  You don't have to do the junctions, which is good.  Don't want to relive some of those with a +100 Warframe!  The enemies are not just +100 in levels.  Their health, shields, and armor have been increased by 250%.  If this makes you NOT want to do it, there is a bright side: both 100% resource drop chance and 100% mod drop chance.  Pretty good trade off!

Luckily, you can turn off the hard mode at any time.  If you feel underpowered on your first mission or so, you are definitely not alone.  This is hard mode after all!  You simply need to re-evaluate your builds, determine if you honestly need to change anything, and in the end realize that these enemies just take a lot more hits to go down.  It wouldn't hurt to actually utilize the mods that are enemy specific, though.  

One cool thing that is offered by Teshin is Honors.  This is where you trade in the collected Steel Essence for various items, such as cosmetics, kuva, relics, or the stance forma blueprint.  Pretty cool stuff!

Happy hunting, Tenno :)