Rare Pull Part 1

Add this game-feel effect to my 2D game: Rare Pull — Color Tease.

Reference scene (context only — map it onto my own characters and sizes):
A capsule reveal repeating every second; t = 0 is the opening. View: 438×190px, night sky, ground 34px above the bottom. A watching hero (80px in) hops 16px at each opening. The capsule (84×78px, purple top, white bottom) sits at 60% of the width. It falls in from above at t = −0.5, lands at t = −0.32 (easeInCubic), hops 16px until t = −0.18, then rests. At t = 0 its halves fly apart and fade (0.32s); a gem prize (54×48px) pops in 80px above the ground with a gold glow, under 4 rarity stars (27×30px, 30px apart) 26px from the top. All clears by t = 0.5. Pulls are gold #FFC24B; 2 in 12 are rainbow (star prize, 5 stars, hue cycling 720°/s). Art is pixel art: the hero is 12×13 art pixels drawn at 7px (84×91px on screen). All sizes are screen px at that scale, so scale them to your own sprite size.

The effect:
Tease the rarity with the capsule's glow before it opens. From t = −0.5 until t = 0, draw two additive radial glows (color at the center, transparent at the edge) centered on the capsule, behind the hero and capsule: radius 120px at opacity 0.8 + 0.2·sin(2π·6t), and radius 60px at opacity 0.6. The color steps through three stages: blue #4AA8FF until t = −0.27, purple #9B7BFF until t = −0.11, then gold #FFC24B until the opening. If the coming pull is rainbow, the last stage cycles hue at 900°/s (95% saturation, 62% lightness) instead of using gold. From t = −0.4, also draw a ring of 6px squares (snapped to a 3px grid) in the stage color on top of the capsule, following it as it drops and bounces: radius 48 + 3·sin(2π·8t) px, opacity 0.9. At t = 0, burst a ring of 6px squares from radius 30 to 100px over 0.12s (easeOutCubic, 1−(1−k)³), with opacity 1 → 0 linearly, in gold or rainbow. Choose the colors from the rarity of the pull about to open. Clear everything after 0.12s so it can play again.

Make it a reusable effect with its numbers exposed as parameters, triggered by one call (for example on hit, on pickup or on landing). Use my engine's normal tools (tweens, timers, particles, shaders). If you don't know which engine I use, ask me first.