First of all, the oracle will not give you a malignant cell because it will only give you a creature from the element the spinner chooses, and "other" is not on the spinner.
Back on topic. Vast majority of times, pets don't really do anything except drawing out a single creature control card from the enemy. Most of the times I get the weakest creature of the element spun, like ash eaters, dragonflies, photons, sparks and such. But when the pet shows as "???" things tend to get interesting. When pet is ???, I've got dragons as pet and some other creatures. Once phase spider as pet and faced chaos lord, he mutated the spider on first turn, turning it into a burrowed graboid with growth ability. By late game, the graboid has about 30/30ish stat, draining my opponents quanta effectively through dissipation shield. So, I would say mostly pets don't do very much, but they sometimes help BIGTIME.