Enemy Spawn Part 1

Add this game-feel effect to my 2D game: Enemy Spawn — Summon Circle.

Reference scene (context only — map it onto my own characters and sizes):
A side view of a 2D night scene with a fixed camera. Art is pixel art: the hero is 12×13 art pixels drawn at 7px (84×91px on screen); the enemy slime is 16×12 art pixels at 7px (112×84px). All sizes below are screen pixels at that scale inside a 438×190px view — scale them to your own sprites. Times are seconds, t = 0 is the moment the enemy appears. The hero stands 80px from the left edge facing right, breathing (height ±2%, 2 per second). One enemy appears every second at a spawn point 286px from the left edge, standing on the ground. After appearing it idles with small bounces (5% squash, 2.5 per second) until 0.32s, crouches to 114% width / 86% height by 0.4s, then hops right off-screen from 0.4s to 0.65s on a 52px arc. Effects that warn before the spawn run in the 0.45s before t = 0.

The effect:
Over the 0.4s before the spawn, open a flat pixel ellipse on the ground at the spawn point: x-radius 0 → 66px (easeOutCubic, 1−(1−k)³), y-radius 0.3 × that, drawn as 6px mint #5BE3B0 squares rotating 0.5 turn/s, with an inner gold #FFC24B ring of 3px dots at 62% of the radius rotating the other way at 1 turn/s. …

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