Is Thriving Rats legal in Standard, Modern, and Commander?

Thriving Rats is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper.

What type of card is Thriving Rats?

Thriving Rats is a Creature — Rat. Its oracle text reads: "When this creature enters, you get {E}{E} (two energy counters). Whenever this creature attacks, you may pay {E}{E}. If you do, put a +1/+1 counter on it. *In Ghirapur, even the lowliest residents live in lavish surroundings.* Power/Toughness: 1/2"