Sinew Eater

Equip creature {3}
Equip Legendary creature {1}
Whenever equipped creature attacks for the first time each turn, untap all creatures you control. There is an additional combat phase after this phase, followed by an additional main phase.
Whenever equipped creature attacks alone, it gets +X/+X until end of turn, where X is the number of non-land permanents you control.
Equipped creature has Hexproof and Trample