When a pack will not start, the launcher finds the mod that breaks it; your worlds are backed up after every game; you see what you changed against the pack and can undo each change.

When the game will not start

Find the culprit: the launcher starts the game with half of the mods, then half of that, until it finds the mod the game cannot start with — in a copy of the instance, so yours is never touched. It respects dependencies, says which mods need the culprit, and switches nothing off until you confirm (files are renamed to .disabled, never deleted). In the crash window and in the instance's Overview.
Safe start: one start without shaders and without mods that only change how the game looks or feels; everything is put back when the game closes.
Copy log in the crash window puts this run's crash report and the whole latest.log on the clipboard (tokens and your folder name hidden) and tells you where it goes: paste it with Ctrl+V into a ticket on the Discord of your server or modpack, or on the STYGION Discord. Discord turns a long log into a file by itself.

Worlds kept safe

After the game closes, every world you played is backed up automatically (on by default, 5 per world, in Settings → Game). Unchanged files are shared between backups, so each new one takes only what changed. Restore one world from Worlds; the current state is backed up first, and even a deleted world can come back.

My changes and disk

New My changes tab for modpack instances: configs and mods that differ from the pack as installed, each with Undo.
Space on disk in the Overview: mods, each world, logs, backups; clear old logs. The instance size is no longer 0 MB.
A modpack's mods are read-only until you allow changes in the instance settings (like the CurseForge app), so pack updates keep working.

Accounts

The Accounts window shows how the Microsoft sign-in stands — signed in, offline, Microsoft outage or sign in again — and what still works without it. A failed sign-in before playing offers Play without signing in (singleplayer, LAN, servers that do not check accounts). The game starts without a round trip to Microsoft while the last sign-in is valid, and keeps joining servers during an outage on a token from the last day.

Graphics, benchmark, servers

On notebooks with two graphics chips the game runs on the dedicated graphics card (on by default; Settings → Game, or per instance).
The benchmark window lists its steps with what each measures, the time and how busy the CPU and GPU are. The test measures in a singleplayer world, with no separate server running next to the game.
Vote for a server in its detail, when its Keystone lists vote sites; presets a server recommends are marked in the Presets tab.

Speed

Measured on a notebook (i7, 16 threads): start to a usable window 0.45–0.52 s (0.12.1: 0.43–0.84 s), Play to a running game 0.4 s for a pack with 384 mods, no screen of the instance detail waits more than 0.12 s; only CurseForge and Modrinth answers take longer (0.3–1.2 s). Ten benchmark calls no longer run on the thread that paints the window, and the STYGION ID sign-in is read from the system keyring once per run instead of on every screen — a keyring that answers slowly no longer freezes the window.

Memory

Auto memory now takes what the pack or the server recommends (STYGION: Aeronautics: 8 GB), but never more than 55 % of your computer's RAM, and says why in the instance settings. Without a recommendation a modded game gets at most 8 GB (was 12 GB): more only made long sessions stutter and froze whole computers. The game starts with half of that and grows when it needs to (-Xms is no longer equal to -Xmx). Your own number still wins, with a warning above 8 GB.

Leaderboard, layout, tickets

Click a player on the badge leaderboard to open their profile: hours played this season, rare badges and the badges they reached.
On a large or 4K screen the interface grows with the window (Settings → Appearance, can be turned off); pages use more of a wide window and pack cards no longer cut off the Install button.
A ticket from Settings → Support can carry the end of an instance's last game log, where the error is.
Opening a pack from an author's page now shows the pack; pressing Discover again returns to the catalogue.
Linux: if the window's page crashes twice within minutes, the next start draws without the graphics card (Settings → Appearance switches it back).

Fixed

The benchmark on Windows measured on the integrated graphics while the game played on the dedicated card.
A launch on Windows could fail with "The process cannot access the file because it is being used by another process" when the game from the same instance still held its libraries; the launcher now waits a moment and, if the file stays locked, says which game holds it.
When a benchmark fails, logs/bench-failed.log now also holds the game's last output and the JVM's fatal error log, so a crash in native code (seen on Windows with Sable's physics) can be told apart.
Cancelling a CurseForge download and a game that crashed are no longer sent as launcher errors; a Fabric "recommends …, which is missing" warning is no longer named as the cause of a crash.
Update in “There is a newer version” before playing did nothing or ended in an error (mc_version of undefined — the most frequent error report since 0.12); it now updates the pack and starts the game.
Play on STYGION MC (and on a server's pack) offered to install the pack again when it was already installed in another version; it now offers to update yours.
Joining a server from Home or Servers used the first instance the server was saved in — even a vanilla one — so the game started “in vanilla” with only the recommended mod. It now joins with the server's pack.
“Finish” on an interrupted pack update did not open the update.
The crash window sometimes read the log before the game's last lines (the error itself) were written, so it said “unknown error” and the copied log ended before the error.

STYGION Launcher s0.13.0: what's new