Activating Volrath's last ability causes it to lose its first ability until your next turn, so if you activate it before the beginning of combat step, it won't trigger during that turn. Players can cast instant spells and activate abilities (such as the second ability) during the beginning of combat step after that first ability has triggered or resolved but before attackers are chosen in the declare attackers step.

If a creature has +1/+1 counters and -1/-1 counters on it, state-based actions remove the same number of each so that it has only one of those kinds of counters on it. This may cause the creature to no longer have any counters on it.

Volrath copies the printed values of the target creature, plus any copy effects that have been applied to it. It won't copy counters on that creature. It also won't copy any effects that have changed its power, toughness, types, color, or so on. Notably, it won't copy effects that made the target become a creature if it's not normally a creature.

If Volrath becomes a copy of a face-down creature, Volrath becomes a 7/5 creature with no color, cost, or creature type. Volrath is still face up.

If Volrath copies a creature that's copying something else, it will become whatever the target is copying.

If the target creature is a token, Volrath copies the original characteristics of that token as stated by the effect that created the token. Volrath doesn't become a token in this case.

If an effect begins to apply to Volrath before it becomes a copy of another creature, that effect will continue to apply.

If Volrath copies a creature the same turn Volrath enters the battlefield, you can't attack with it or use any of its {T} abilities (if it gains any) unless the copied creature has haste.

If Volrath becomes a copy of a legendary creature you control, you'll put one of them into your graveyard.

If another object becomes a copy of Volrath, it has the ability to become a copy of something else and it's 7/5.

If Volrath becomes a copy of a creature whose power and toughness are defined by an ability (usually printed as */* or similar), Volrath doesn't copy the ability that defines its power and toughness. Volrath remains a 7/5 creature.

If Volrath copies a creature with an ability that can be activated only once each turn (such as Chainer, Nightmare Adept), you can activate that ability once. If Volrath then becomes a copy of that same creature, you can activate that ability another time, and so on.