Crocodile

Crocodile (Epic rarity) belongs to the Jungle zone. Jungle is zone 4 of 11 on the normal route; the wiki lists its entry requirement as ~40K speed, and the nests there are watched by the Tiger. You get it by carrying the Crocodile Egg back to your pen.

At $420/s base income, Crocodile sits 6th out of 8 in its zone — King Snake tops the Jungle at $3.5M/s. The listed figure assumes no mutation and a normal weight.

With a colour mutation and no size bonus, the same Crocodile would earn roughly: Silver ×1.2 ≈ $504/s, Golden ×2.5 ≈ $1.05K/s, Rainbow ×3.5 ≈ $1.47K/s (multipliers from the wiki's Mutations page; arithmetic is ours). Add a Giant (×3) or Huge (×5) size roll on top and the numbers multiply again.

Hatching it pays a one-off reward of +9k Speed, $42k, and the egg takes 1m to grow in the pen. That reward is the reason low-income eggs are still worth stealing early: the speed bonus is what gets you into the next zone.

Epics are the mid-tier of their zone — a good candidate for your first mutation roll because the base rate is high enough to matter.