Donkey Kong Country 2: Diddy's Kong Quest/Levels/Topsail Trouble
With the snake, you can reach bananas above the start, as well as the letter K to the left. Jump up to the next platforms. then head right to jump up again. At the top of this mast, you can reach a bonus game to kill dragonflies, but you need to jump off the snake and throw your companion to reach this barrel.
The letter O also requires a snake jump.
Past the half-way barrel, you will start to climb ropes. On the second set of ropes, head to the right and climb down for the letter N.
The letter G is available at the end of the level, by timing your jump correctly.