One thing that's really worth noting about Lava Reef Zone is that Sonic and Knuckles are confined to nearly completely different routes to each other in both Acts - or so it may seem at first anyway. In Act 1, Sonic has the ability to explore most of the space, with his route splintering into a couple of significant choices of sub-routes towards the end, while Knuckles meanwhile appears to have a largely single-route path to himself that's literally crammed into the bottom of the stage, and takes place mostly inside the internal passages. The two meet near the end and Knuckles' tasks are quite a bit more challenging here. What you might not know is that Knuckles can actually access the majority of Sonic's routes too, by making use of a very well hidden stairway, described in Point #1, accessible if you can bypass the large drilling badnik near the start. Act 2 mostly keeps the characters to their own separate journeys once again, Knuckles still having to deal with some genuinely difficult sections, but at least his take on both acts are a lot shorter than Sonic's, and in Act 2, he doesn't even have a boss to fight! There are fewer multiple routes in Act 2, but those not afraid to explore may find one or two shortcuts if they look hard enough - a particularly big one for Sonic near the start. There are no death drops, except for below the thin walkway at the very end, in a huge open section. Still, this is a pretty difficult level for either character, though at the same time, Act 1 in particular is still a fun and lively stage to play.

Eggman robots to encounter include Toxomister, Fireworm and an unnamed exploding badnik. Toxomister are the strange grey poles sticking out of the ground, reaching just above your character's head and with a single lazy looking eye mounted on the top, which you need to hit in order to defeat them. They can also be found upside down on the ceilings. They don't go anywhere and aren't very animated - as to be expected from a pole really - but they do produce small clouds of nasty toxic gas in their immediate area, which float down and attach to you if you make contact. Similar to the piranhas of Hydrocity, when the cloud is on you, your speed will dramatically reduce, you won't be able to jump very high, and worse, your ring count will begin to drop by one per second until it kills you. To free yourself, either kill the badnik, spin dash away, or quickly move from left to right. They're a real danger actually, not just if you're low on rings when you find yourself under the cloud, but all you need to do is take one hit from something else, and then the cloud will be able to kill you instantly. Don't think it won't! Fireworms are usually found inside the tunnels and are like flying Caterkillers, sometimes grouped in pairs. They emerge from small, well hidden black holes in the background wall, so be careful as they can take you by surprise when they first emerge. They then proceed to float back and forth, producing small flames from their wriggling spiked body parts, so hit them on the heads only please. The third badnik - "Iwamodoki" in Japanese, but unnamed in English - is a self-harming one that hides under rocks that stick out of the ground, and peaks out when you get close. At this point, you will have set them off and they begin to flash. You've got about three seconds before they explode, throwing harmful chunks of rock a fair distance around them, and you can tell that they're about to pop when their eyes open up wide. You cannot harm this badnik yourself, but if you've got a shield (and a good player usually will, in this stage), the pieces of rock will just bounce right off, causing you zero discomfort. Very useful, considering the vast number of these exploders.

- There's a strong theory regarding the part Knuckles plays during his playable story through Sonic 3/Sonic & Knuckles. There's reasonable evidence, particularly in this level and the following one, that suggests his story actually takes place completely after Sonic's has finished, constraining it simply to a "clean-up" operation across the island in which the aim is to defeat the remaining badniks, including one particularly resilient and confident Eggrobo. At the end of Act 2, Sonic clearly approaches the Death Egg, as it peers through the open volcano in the ceiling, yet it's no longer there when Knuckles comes to the exact same spot - presumably having already been launched. The same can be said for its appearance in the upper background of the next level, Hidden Palace, where the light coming through highlights it even more clearly. In Act 1, Knuckles' exclusive route is contained almost entirely within internal sections where the background (which also normally contains the Death Egg) can't be seen. However the theory stumbles slightly if you take the very secret alternate route described in Point #1 which redirects Knuckles onto the vast majority of Sonic's route. Vexingly, by Point #4 as Knuckles, you will then see the Death Egg in the background, with a method that's perfectly above board. Nothing has ever been officially clarified, but nevertheless, I would say there is enough other evidence throughout the game to suggest this theory to be true, and that perhaps this was an oversight on the part of the developers.