|Coins from Enemies
Due to the split areas in Lethal Lava Land, you will likely have to visit the inside of the volcano in order to get 100 coins, although there is a total of 107 coins. That leaves a total of 26 coins inside of the volcano, although two of those are from Bullies, with a rather bad placement, so grabbing those coins is not something you want to do. That boils down to 24 coins inside of the volcano, so make plans to have at least 76 coins before entering it. It is best to do this star on either Hot-Foot-It Into the Volcano or Elevator Tour in the Volcano, as the Koopa shell in the yellow box will spawn near the beginning of the course. This allows you to easily gather some of the coins in the outside area, but the box with the shell doesn’t respawn, so you have to be careful not to lose it.
When you start out on the course, head to the arch and cross the first bridge to find the first Bully. Knock it into the lava and hope the coin flies onto the platform, so you can collect it (1). You should be at the fork, so head across the moving bridge and defeat the Mr. I there for another five coins (6). You can jump onto the crescent-shaped ramp nearby to get three coins, as well as five more from the “bridge” with the fluctuating lava (14). You should now be before the sliding Bowser puzzle, where you can collect all eight Red Coins (30). Note that once the puzzle completes itself once when you’re on it, five coins will pop out the middle of it (35)
There are another two Bullies before the platform with the Fire Bars, as well as four coins on another crescent-shaped ramp (41). Jump onto the platform with the spinning Fire Bars and onto the next submerging spot, where you can collect five more coins (46). The first Big Bully has no coins, but you might need to get rid of it until the moving platform that gets you to the second Big Bully platform arrives. There will be three normal Bullies here, as well as a ring of coins (57). Do whatever you want with the Big Bully that spawns, then it’s time to collect more coins.
There will be four coins on the square-shaped pieces that get submerged in lava (61). From there, you should be able to Long Jump to the circular island with the Mr. I, where you not only get a Blue Coin from it, but also eight more coins (74). There is one of those bouncing boxes, when you grab it, on the serpent-like walkway, but it might be better to ignore it. While you can get five coins from it, there’s not a good place to bounce to, so whether you do it or not is up to you (79). The little path leading to the volcano will have another five coins, then there will three more on the ring surrounding the volcano (87).
Alright, if you have a good number of coins, 80+ or so, then you can probably go inside of the volcano now. If you want a little more insurance, return to the start and grab the Koopa shell from the yellow box. There will be five coins on one of the high brown ramps (the one by the three Bullies platform), as well as five more coins underneath the opening/closing bridge (97). Go inside the volcano now.
Behind your starting position, in the volcano, there will be a single coin right before the elevator (98). Feel free to use the elevators to get to the Elevator Tour star, where there will be three coins right before it (101). Find a spot where you can jump back down towards the starting point of the volcano, then begin going along the other path. There will be ten coins before the bit of the wall that drops down to try and crush you (111). Forget about the Bully here, though, as it would be super difficult to collect the coin it leaves behind after knocking it into the lava. There will be another five coins before next Bully and lavafall, then five more on the thin ledge by the lavafall (121). That will be all of the coins, so collect either of the two normal stars to finish.