The location checks for this game are every monitor, all six bosses and all six special zones.
This world will add to the item pool 6 emeralds, 14 keys, 2 buff items (more on those in a moment), rings, and filler.
There are 6 keys for the normal zones, 1 for the Final Zone, 1 for Specials access, and 6 for the special stages themselves.
The player will start with the Specials access key and one random normal zone key unlocked, the remaining 12 are in the pool.
The 195 possible rings are split into 10 classed as Useful and 185 classed as Filler, the hope is that this will balance the distribution.
To complete the world you need to complete the 6 specials, 6 bosses, get the 6 emeralds in the pool, and some amount of the pool rings.
The number of rings added to the pool is set by an option, the remaining item slots will contain junk items.

What changes to Sonic 1 you need to know about

To make this sane to play you start in level select and get kicked back there after a level.
Monitor breaking is persistent and all of them are now ring boxes. This will slightly increase difficulty.
Special stages will play in order, you won't move on to the next until you pass one.
If you take damage and when you enter a level the mod will treat your AP received Ring count as your minimum instead of 0.
With the AP ring gift, you can survive any damage that would make you drop rings, like you immediately pick up additional rings.
To save rom space, Sonic hurt from an enemy will drop 6 rings and reset to the AP count as long as you have at least 1 ring.
You are not immune to instant deaths like squishing, time out and drowning.
Spikes floors are potentially more dangerous, they can lock you into a bounce loop instead of killing you.
Pause a level and press C to exit back to level select.
A basic spin dash has been added to make life a little less miserable.
You don't lose lives when dying, since it makes no sense in this context.
Repeating a boss doesn't give you extra rewards.
You don't gain extra lives for 100 rings, but you can't lose lives either.
Completing a stage with 50 rings won't spawn a giant ring due to progression gating.
Completing acts 2 or 3 of Scrap Brain won't advance you to the next zone.
You start with a random zone unlocked, further zone unlocks are via keys in other players' pools
The 50 ring secret upper path on SBZ2 is disabled as there are no checks up there.
Special stage buffs: The UP block is disabled, no speeding up. Goal and R blocks can be disabled using the two buff items in the pool.
ReadySonic's "Roll into Catakiller" fix has been included, so you can kill them by rolling into them.
ReadySonic's "High speed camera fix" has also been included to hopefully make things a little safer.

Setup

The supplied patch is applied against the Sonic 1 world REV0 release (Sonic The Hedgehog (W) (REV00))
Downgrade patches are also supplied, if you need to turn REV1 into REV0.
The game state is tracked via SRAM, this includes the game seed to keep stale saves from messing up new runs.
It is recommended, if you have save data from a previous attempt, to use the RESET SAVE level select option before connecting to the server.
Resetting mid run will result in the client writing the progress that has been received from the AP server.
The level select will currently only rerender the progress indicators when you press an input button, just press up or down after reset.
The server reapplying saved progress (after a save reset) while in a level may result in problems, it's strongly advised to avoid doing so.
The most likely bug I've missed from patching is some oddity in how rings are reset after taking damage. Let me know if you can get silly numbers consistently.

TODO/Missing features

The code will probably need a little cleanup.
Worth adding item received messages via BizHawk Client's message feature? Feedback welcome on that