Perfect bonus

The perfect bonus is an additional score bonus that rewards players with 50,000 points if they collect all rings on the map, including Super Ring Monitors, and finish the level without losing any of them. In a regular playthrough, the perfect bonus is useful because it gives the player an automatic extra life from the score bonus (plus additional extra lives after collecting the 100th and 200th ring). In Record Attack, it is useful when trying for a high score.

Whether or not a perfect bonus is awarded in a level is set by the BonusType parameter in the level header. The perfect bonus is awarded if the parameter is set to Normal (for regular levels) or ERZ3 (for regular levels with a boss at the end). It is not awarded if the parameter is set to Boss (for boss levels, where getting a perfect bonus would usually be trivially easy), NiGHTS, NiGHTSLink (for NiGHTS levels, where rings respawn), or None (no bonuses at all).

In the Record Attack menu, the ring count of levels where all rings have been collected is colored yellow, regardless of whether the level awards a perfect bonus or not.

Via the ME_PERFECT flag, it is possible to award a custom emblem for achieving a perfect bonus in a specific map.

Perfect bonus in SRB2's levels

You can attain a perfect bonus in all but two stages. Arid Canyon Zone Act 2 and Haunted Heights Zone are impossible because no character can access all paths, even with backtracking.

Level	Rings	Info
Greenflower Zone Act 1	453	This is the easiest stage to get a perfect bonus in, since the ring requirement is low and there are few hidden rings. All the characters can get the perfect bonus. Non-flying characters can reach the 8 rings above where the Armageddon Shield is with the Whirlwind Shield, or a few successful badnik bounces from where the Attraction Shield monitor is. However, Fang is required to use the Whirlwind Shield. He can get to the ledge by jumping off the house behind the Attraction Shield and using the second jump at his apex.
Greenflower Zone Act 2	733	Amy is required to achieve this perfect bonus, as she is the only character who can access the entire level. Reaching the highest cliff with the Force Shield up top requires hitting the diagonal red spring on the ground near the picnic with Amy's hammer and either having a Whirlwind Shield or Super Sneakers to make it up top. Having both yields the best results. You can easily reach the cave with 8 ring monitors by hitting the spring that's in the river where the Elemental Shield is, and landing on the edge before the cave entrance. A Whirlwind Shield is required to get in there.
Techno Hill Zone Act 1	878	Only Tails and Knuckles can get a perfect bonus in this stage. Before the room that contains Knuckles' split path, you should have 231 rings. Collect the 9 rings that Knuckles can grab for a round 240 before continuing onto his path. Knuckles' path has 154 rings, not counting the ones above the Attraction Shield. As Knuckles, remember to go back to the room with the split path to grab the 21 rings you couldn't before. Tread across the pools of goop with the Attraction Shield to quickly grab submerged rings; use the Elemental Shield's stomp ability to quickly grab submerged ring monitors. There are two Attraction Shields in the level; make good use of them before breaking submerged ring monitors.
Techno Hill Zone Act 2	924	Knuckles is required to achieve this perfect bonus, as there are rings in a Knuckles-exclusive path at the beginning, as well as ring monitors behind bustable walls in the room before the Turret/conveyor split. Much like Act 1, there are some rings submerged in goop that are most efficiently collected using an Attraction Shield, and ring monitors under goop best collected using an Elemental Shield. The level has four Attraction Shields, which is more than enough if you use them as effectively as possible. In the large open room near the end, the eight rings surrounding an Emerald Token under goop are most easily collected using an Attraction Shield plus the invincibility found on a ledge near the end of the Deton path. Climb down the wall in the goop and attract the rings before invincibility runs out.
Deep Sea Zone Act 1	836	All characters can get a perfect bonus in this level. Sonic, Metal Sonic, Amy and Fang can only backtrack if the middle path is opened up first -- on that same note, Amy and Fang are only able to backtrack through this path with a well-timed double jump through the use of the Whirlwind Shield. Keep hold of an Attraction Shield before getting to the three circles of rings if you're not Tails or Knuckles.
Deep Sea Zone Act 2	1005	Amy and a constant hold on a Whirlwind Shield is required to get a perfect bonus in this stage. You want to open the door near the beginning and open the door at the end of that path to be able grab all the rings at the beginning. You can't take the crusher path first because that will lock you out of backtracking. You need to take the right path where the waterslide splits and open up that door to be able to backtrack from the ending. There are two Whirlwind Shields that Amy can access without assistance: one before the waterslide finale, and one near the exit. You need to do precise double jumps with the Whirlwind Shield to backtrack out of the waterslide. Use the Whirlwind Shield to backtrack to places you haven't gone to yet.
Castle Eggman Zone Act 1	912
Castle Eggman Zone Act 2	1279
Arid Canyon Zone Act 1	713	Due to this stage's open nature, there are many rings hidden in places that are easy to overlook.
Red Volcano Zone Act 1	501
Egg Rock Zone Act 1	624	An Attraction Shield is required for some of the rings in this stage, so make sure to always carry one and don't lose it. There are rings on all three routes of the character-specific split on the left path. The best choice here is Tails, since he can backtrack through Knuckles' path and use the Super Sneakers right behind the point of the split to get through Sonic's crusher gauntlet. The zoom tube that leads to the outdoor room at the end of the left path is one-way. Since the left path is shorter, it is recommended that you first take the left path up until the zoom tube, then backtrack and take the right path, and finally enter the outdoor room from the exit to get the remaining rings.
Egg Rock Zone Act 2	686	Near the end sign is a corridor that leads back to the beginning of the stage, allowing you to go through both paths without backtracking.
Black Core Zone Act 1	128	After the drop near the beginning, there is an Attraction Shield hidden behind the first pillar next to the rightmost wall. After finishing the race, the timer disappears, allowing you to backtrack through the stage and collect any remaining rings.
Frozen Hillside Zone	488
Pipe Towers Zone	422	This level has three pipes that act as one-way passages. At the transitions, you should have 163, 248, and 313 rings, respectively.
Forest Fortress Zone	644
Techno Legacy Zone	179
Aerial Garden Zone	1189	This stage is extremely large and has many hidden areas that contains additional rings, but there are no one-way passages and few hazards besides death pits, so the stage is fairly convenient to explore as Tails.
Azure Temple Zone	906	Knuckles is required for this stage because there are rings on his path. Multiple routes cannot be backtracked and therefore must be done in order. At the last path split, the puzzle route must be completed before the current route or it will become impossible to backtrack. You can move many of the gargoyles to disarm them for backtracking purposes.