Butter Bridge 1 is the first level on Butter Bridge that is in the Twin Bridges area. It is unlocked after beating Vanilla Fortress. This level takes place in an aerial setting, and is also an autoscrolling level.
The player starts on a mushroom platform with a small bridge piece at the end. After that, the player should keep jumping to the tall mushroom pairs that extend when the player hops on one, and avoiding the Koopa Paratroopa floating in the middle of the second pair. The player must hop on a grey falling platform and collect the first Dragon Coin, then jump on a few more mushrooms with a grey platform in the middle of one of them, and then jumping on a Koopa Paratroopa to get to a higher point where the second Dragon Coin can be obtained, with the third Dragon Coin just right next to it in the middle of more mushrooms. After this, the player will come across a line of green Koopa Paratroopas, following them are more mushrooms that get higher and higher. Between the last two mushrooms is the fourth Dragon Coin, that can easily be obtained when the last mushroom extends low enough (there are also three green Koopa Paratroopas flying by too).
After this section, the player will next make their way to an upwards section with yellow Rotating Blocks, with a single ? Block at the bottom. A little known secret is that inside the second-to-most-left block at the very top, is a 1-up Mushroom. Once the player climbs up this area, they should continue on and jump across the mushroom pair and hop onto the grey platform that falls, with the fifth Dragon Coin right beside it. The platform will fall and take the player to a bridge, where they'll encounter more Koopa Paratroopas. They should go right to the purple Warp Pipe which takes them to the Goal Pole (that they must jump to from a pipe on top of a bridge). Beside this pipe, is a Bonus Block, and in Super Mario Advance 2, there is a Message Block that says the following:
Try striking a bonus block AFTER you have found at least 30 coins in an area...