Countdown Part 1

Add this game-feel effect to my 2D game: Countdown — Zoom Slam.

Reference scene (context only — map it onto my own characters and sizes):
A side view at a race start line: a checkered strip (12×6px squares, 2 rows, cream and dark brown) along the ground. Art is pixel art: the hero is 12×13 art pixels drawn at 7px (about 84×91px on screen) on the left, the slime 16×12 art pixels at 7px on the right, 284px apart. All sizes below are screen pixels at that scale — scale them to your own sprite size. Times are seconds, t = 0 is the moment a new count appears. Once per second the next count appears in the middle: 3, 2, 1, GO, then it repeats. Counts use a 3×5 pixel font with 16px cells (80px tall), cream #fff6d8 with a dark #1a1014 outline; GO uses 14px cells in mint #5BE3B0. On 3, 2 and 1 both racers do a small crouch (6–8% shorter, recovering in 0.2s); on GO they hop (hero 34px, slime 26px, over 0.4s) — this part is the same in all six.

The effect:
Each count starts at 300% scale (GO: 350%) and 60% opacity, and slams down to 100% in 0.12s with easeInCubic (k³), slow then fast, like it falls onto the screen. …

The rest of this prompt — exact sizes, easing, colors and particle counts — and full prompts 2–6 are in the pack.