Cosmic Biome

The wiki describes Cosmic as one of the final zones of the original progression, and the entry price matches: 700M Speed. Its guardian is the Cosmic Skeleton, which hatches as the Cosmic Skeleton Boss, a Secret worth $45M/s from a 2h 30min egg.

The first Divine in the biome order

Cosmic's eight eggs go from Epic to Divine:

• Centapede (Epic, $1.5K/s, 2m, +960k Speed)
• Cosmic Gecko (Legendary, $30K/s, 4m, +1m)
• Cosmic Gorilla (Mythic, $180K/s, 7m, +1.2m)
• La Vacca Saturno Saturnita (Cosmic, $2.2M/s, 13m, no reward listed)
• Cosmic Skeleton Boss (Secret, $45M/s, 2h 30min, +1.6m)
• Cosmic Dragon (Secret, $60M/s, 3h, +1.4m)
• Eternal Lunar Dragon (Eternal, $250M/s, 7h, +1.9m)
• Unicorn (Divine, $1B/s, 12h, +2.4m)

The Unicorn is the first Divine pet you can steal from a regular biome nest and the lowest-earning of the 14 Divines. Between the two Secrets, the Cosmic Dragon earns a third more, yet the Cosmic Skeleton Boss grows 30 minutes faster and pays more Speed (+1.6m against +1.4m).

Centapede, the Speed egg

Per second of growth, the Centapede returns about 8,000 Speed, nearly double the Cosmic Gecko and far above the 12-hour Unicorn (about 56). Cherry Blossom needs 2.5B, a gap of 1.8B, and the eggs-only route would take 1,875 Centapedes. One of each Cosmic egg adds about 10.5M.

Equipment is what bridges it. The Galaxy Trail (5×) costs $20B, so a single Eternal Lunar Dragon reward ($25b) covers it. The Lucky Block Treadmill (+200 per step) costs $75B, less than one Unicorn reward ($100b).

Cosmic on the Rift banners

Cosmic feeds Riftbeasts and Shattered Rift. On the Rift Sacrifice tiers, Centapede and Cosmic Gecko are Easy, Cosmic Gorilla is Medium, and La Vacca Saturno Saturnita is Hard. That makes La Vacca an unusual case: its egg lists no Speed or cash reward, but a spare copy can fill a Hard sacrifice request.

With the wiki's formula, a Rainbow Unicorn (×3.5) would be in the $3.5B/s range, above any base pet from the next two biomes.