Turtle

The Turtle Egg is the Rare-rarity egg of the Lake, and the pet inside it is Turtle. Lake is zone 2 of 11 on the normal route; the wiki lists its entry requirement as 900 speed, and the nests there are watched by the Swan.

Base income is $60/s. Among the 8 pets tagged Lake on the wiki that puts Turtle at number 5 — Leviathan tops the Lake at $220K/s. Remember the game multiplies this base by the size roll and by the mutation, so two Turtles can earn very different amounts.

With a colour mutation and no size bonus, the same Turtle would earn roughly: Silver ×1.2 ≈ $72/s, Golden ×2.5 ≈ $150/s, Rainbow ×3.5 ≈ $210/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 +2.7k Speed, $6k, and the egg takes 50s 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.

A Rare is usually the first egg in a zone that is worth waiting out the 5-minute nest reset for.