The power to take on the new enemies and bosses in Elden Ring Shadow of the Erdtree won't primarily come from runes. The DLC has its own leveling system that has never existed in a FromSoftware game—although it resembles the one in Sekiro a bit.
In addition to normal rune leveling, you'll find "Scadutree Fragments" in the Land of Shadow that will increase your "Scadutree Blessing" level, scaling your stats up much higher than they would normally. You'll also find catacombs and dungeons with Revered Spirit Ash Blessings to globally increase the power and defense of Torrent and your spirit ash summons past where Glovewort can take you in the base game.
You can still level up with runes, but it'll take a massive amount of them once you push past level 150. And even then, the benefit of each stat point falls off considerably once they're high enough. Scadutree Fragments are the answer to this problem.
The only catch is that your Scadutree Blessing and Revered Spirit Ash Blessing level disappear when you're anywhere outside of the DLC area. Your stats will be highlighted in orange to show that they're enabled and will go back to white when they're not. I imagine this allows FromSoft to more easily balance the difficulty of the DLC areas without trivializing the base game.
Both of these new leveling systems will be familiar if you've played Elden Ring already. Scadutree Fragments and Revered Spirit Ash Blessings work just like Golden Seeds and Sacred Tears do in the base game for leveling up your Crimson and Cerulean flasks: You pick them up and upgrade your level at Graces, with the required amount scaling up as you progress.
Where to find Scadutree Fragments
In our limited time with Shadow of the Erdtree's preview build, we found Scadutree Fragments in a variety of locations, but mostly held by statues of horned figures called "hornsent" (they look suspiciously similar to the Omen). Once you know what you're looking for, these stone figures aren't hard to catch from afar. Some of them have enemies nearby, but most of them felt no different than the mini Erdtrees with Golden Seeds sprinkled throughout the Lands Between.
Scadutree Fragments also showed up in the major dungeons as a reward after a boss or near a significant checkpoint within it. It's possible mini bosses of some kind could drop them too, but we didn't find any in the few hours we had with the DLC.
Where to find Revered Spirit Ash Blessings
The Revered Spirit Ash Blessings, however, were seemingly off of bosses in catacombs and underground dungeons or "gaols" (not to be confused with evergaols). If I had to guess, they will be the reward for doing more of the game's side content than the dungeons on the critical path through the game.
Every Scadutree Blessing level raises all of your stats by a set amount—the math is still unclear but it's a significant boost. Our premade characters for the preview were level 150 with weapons leveled up to +25 and I could tell I was hitting harder after gathering up a bunch of Scadutree Fragments. I can't say I noticed my Spirit Ash summons were noticeably stronger after using a few Revered Spirit Ash Blessings but I was busy testing new ones out, like a spider hand one that heals you. The exact benefits will be more clear once we get our hands on the full DLC.
Shadow of the Erdtree drops on June 20.
