Cavalry Master

Oracle Text

Flanking (Whenever a creature without flanking blocks this creature, the blocking creature gets -1/-1 until end of turn.)

Other creatures you control with flanking have flanking. (Each instance of flanking triggers separately.)

Card Rulings

9/25/2006 Cavalry Master adds only one instance of flanking per creature, even if that creature already has multiple instances of flanking.
9/25/2006 If a creature without flanking is given flanking by another effect, then this ability will grant a second instance. Similarly, if a creature loses flanking, then it won’t get the Calvary Master instance either.