Arni Brokenbrow

The greatest power among other creatures you control is determined as the boast ability resolves. You choose at that time whether you'd like to change Arni Brokenbrow's base power. If you control no other creatures at that time, you can change Arni's base power to 1 until end of turn. Arni objects to this course of action.

If an effect adds additional combat phases to a turn and a creature with a boast ability attacks more than once during that turn, its boast ability can still be activated only once.

In some unfortunate cases, the greatest power among other creatures you control may be negative. For example, if that greatest power is -3, you could change Arni's base power to -2 until end of turn. Arni strenuously objects to this course of action.

If it's not your turn and you gain control of a creature with a boast ability after that creature attacked, you can activate that creature's boast ability if it hasn't been activated yet that turn.

Any effects that modify Arni Brokenbrow's power without setting it to a specific value will apply after Arni's base power is set, regardless of the order in which those effects were created. The same is true of counters that modify Arni's power.

Arni Brokenbrow's new base power is set to the 1 plus the actual power of the other creature you control with the highest power, not that creature's base power. If that creature's power changes after the boast ability has resolved, Arni's power is unaffected.