A wizard character really wants a praying mantis familiar. Not a "giant" one, just a regular-sized one. No particular reason other than he just really likes them. What would be the closest approximation for the stats?
I'd probably just go with a greensting scorpion without the poison.
Diminuative. Tiny is the size of a house cat, diminuative a mouse if I remember correctly. Some mantis species can get that big.
Well, a common mantis would be size 'fine' gamewise, so is not specifically allowed, but would likely be allowable outside of PFS play. I would stat it as a size fine greens ting scorpion, without the poison. That should get the flavor you are looking for. The only real objections I could see would be with its effectiveness with stealth and delivering touch spells with the bonuses from the size modifiers.
I like the style of the concept.
The Thrush (Ultimate Magic) is Diminutive. That might work.