Rhonas the Indomitable

Oracle Text

Deathtouch, indestructible

Rhonas the Indomitable can't attack or block unless you control another creature with power 4 or greater.

2G: Another target creature gets +2/+0 and gains trample until end of turn.

Card Rulings

4/18/2017 Once Rhonas has attacked or blocked, it will remain in combat even if you no longer control another creature with power 4 or greater.
4/18/2017 You don’t have to attack with another creature with power 4 or greater for Rhonas to be able to attack. The same is true of blocking.