Build a complete retro 2D side-scrolling platformer in a single HTML file 
(HTML5 Canvas + vanilla JavaScript, no external libraries or asset files). 
All art must be drawn procedurally with canvas rectangles/pixel data — 
original designs, not copyrighted characters.

CORE FEEL (NES-era physics, tuned to feel like classic platformers):
- Player runs, accelerates gradually, and skids when changing direction.
- Variable jump height: tap = short hop, hold = full jump. Slight air control.
- Gravity ~0.5 px/frame², max fall speed capped, coyote time ~4 frames, 
  jump buffer ~5 frames.
- 60 FPS fixed timestep game loop with delta accumulator.
- Camera scrolls horizontally, locked to the player, never scrolls backward.

PLAYER:
- Character named "Pip", a small overall-wearing plumber-style hero (original 
  design: red cap, blue overalls, 16x16 pixel style drawn with canvas).
- Two states: small and powered-up (bigger, can break brick blocks).
- Taking damage while powered-up reverts to small; damage while small = death.
- 1.5 seconds of invincibility flicker after taking damage.
- 3 lives, respawn at level start (or checkpoint) on death.

ENEMIES:
- "Waddler": walks left, flips direction at walls/ledges, dies when stomped.
- "Spiker": armored, cannot be stomped, must be avoided or hit from below.
- "Hopper": jumps in an arc toward the player.
- Stomping an enemy bounces the player upward.

BLOCKS & ITEMS:
- Solid ground tiles, brick blocks (breakable when powered-up), question 
  blocks (bump from below to release a coin or a power-up mushroom).
- Coins: collect for score, 100 coins = extra life.
- Power-up mushroom slides along the ground when released.
- Pipes as decorative solid obstacles (one enterable pipe in Level 2).
- Bottomless pits = instant death.

LEVEL DESIGN — exactly 3 levels, each ending with a flagpole the player 
slides down for bonus points:
1. "Green Fields" — tutorial level. Flat ground, simple gaps, a few Waddlers, 
   first question block, gentle introduction to jumping and stomping. 
   Easy difficulty, ~90 seconds.
2. "Cavern Depths" — underground theme (dark blue palette). Low ceilings, 
   tighter jumps, Spikers, moving platforms, one hidden bonus room with coins. 
   Medium difficulty, ~120 seconds.
3. "Sky Castle" — hardest. Floating platforms over pits, Hoppers, a vertical 
   climbing section, a final boss: a large jumping enemy that must be hit 
   3 times by bouncing on it while dodging projectiles. ~150 seconds.

Store each level as a tile-based array (e.g. character grid strings) so 
layouts are easy to edit.

HUD & FLOW:
- Top bar: SCORE, COINS, WORLD (1-1, 1-2, 1-3), TIME countdown, LIVES.
- Title screen with "PRESS ENTER TO START".
- Level complete screen showing score, then auto-advance.
- Game over screen with restart option.
- Timer reaching zero = death.

CONTROLS:
- Arrow keys / A-D to move, Space or Up or W to jump, Shift to run faster.
- P to pause.

AUDIO:
- Generate simple chiptune-style sounds with the Web Audio API 
  (square/triangle oscillators): jump, coin, stomp, power-up, death, 
  level clear. No external audio files. Include a mute toggle (M).

POLISH:
- Pixel-perfect rendering (imageSmoothingEnabled = false), integer scaling.
- Parallax background (clouds/hills for level 1, stalactites for 2, 
  distant sky for 3).
- Screen shake on boss hits, particle burst on brick break.
- Comment the code clearly and organize it into sections: 
  constants, input, entities, physics, levels, rendering, game loop.

Deliver the full working code in one file, ready to open in a browser.