Arahbo, Roar of the World
Legendary Creature — Cat Avatar
Eminence — At the beginning of combat on your turn, if Arahbo is in the command zone or on the battlefield, another target Cat you control gets +3/+3 until end of turn.
Whenever another Cat you control attacks, you may pay 
. If you do, it gains trample and gets +X/+X until end of turn, where X is its power.
Jesper Ejsing
Rulings
Once either of Arahbo's triggered abilities has resolved, the affected Cat keeps its bonus even if Arahbo changes zones later in the turn.
(wotc • 2017-08-25)
This commander's eminence ability is a triggered ability. The commander must be on the battlefield or in the command zone as the trigger event occurs and also as the triggered ability resolves. If the commander is in an appropriate zone as the trigger event occurs but leaves that zone, the ability won't do anything as it resolves.
(wotc • 2017-08-25)
Notably, if your commander is on the battlefield and its eminence ability triggers, but it's put into the command zone before that ability resolves, that ability won't do anything as it resolves. This is because an object that changes zones is considered a new object.
(wotc • 2017-08-25)
If multiple Cats attack, Arahbo's last ability triggers that many times. You may pay {1}{G}{W} each time one resolves.
(wotc • 2017-08-25)
The value of X is determined only as Arahbo's last ability resolves. If the attacking Cat's power is negative at that time, X is 0.
(wotc • 2017-08-25)
While resolving Arahbo's last ability, you can't pay {1}{G}{W} multiple times to multiply the effect for one Cat.
(wotc • 2017-08-25)
If a Cat you control enters the battlefield attacking, it won't cause Arahbo's last ability to trigger.
(wotc • 2017-08-25)
Rulings
Once either of Arahbo's triggered abilities has resolved, the affected Cat keeps its bonus even if Arahbo changes zones later in the turn.
(wotc • 2017-08-25)
This commander's eminence ability is a triggered ability. The commander must be on the battlefield or in the command zone as the trigger event occurs and also as the triggered ability resolves. If the commander is in an appropriate zone as the trigger event occurs but leaves that zone, the ability won't do anything as it resolves.
(wotc • 2017-08-25)
Notably, if your commander is on the battlefield and its eminence ability triggers, but it's put into the command zone before that ability resolves, that ability won't do anything as it resolves. This is because an object that changes zones is considered a new object.
(wotc • 2017-08-25)
If multiple Cats attack, Arahbo's last ability triggers that many times. You may pay {1}{G}{W} each time one resolves.
(wotc • 2017-08-25)
The value of X is determined only as Arahbo's last ability resolves. If the attacking Cat's power is negative at that time, X is 0.
(wotc • 2017-08-25)
While resolving Arahbo's last ability, you can't pay {1}{G}{W} multiple times to multiply the effect for one Cat.
(wotc • 2017-08-25)
If a Cat you control enters the battlefield attacking, it won't cause Arahbo's last ability to trigger.
(wotc • 2017-08-25)