Index Reward Pets are a special category of pets. The only way to obtain them aside from trading is to obtain every pet from their respective world. It only counts if a player hatches the pet from an egg and not from trading. A player can also get a shiny version of the pet by hatching or making all the shiny pets of their respective world.
Each pet excluding the Crazy Cat Stack (which has x1,000 less in its 4th multiplier) has the same exact stats except for differences with the world currency and they are all tradeable.