Is Silkguard legal in Standard, Modern, and Commander?

Silkguard is legal in: Legacy, Vintage, Commander, Historic.

Silkguard

Q: What type of card is Silkguard?

Silkguard is an Instant. Its oracle text reads: "Put a +1/+1 counter on each of up to X target creatures you control. Auras, Equipment, and modified creatures you control gain hexproof until end of turn. (Equipment, Auras you control, and counters are modifications.)"