Do I must have already attacking/blocking unit to use Striking the grudge? Or if I use this tactic in my for example Quest or Kingdom phase, can I give it's bonus to one of my unit? The same goes for Waaagh! and Grudge Thrower.
Striking the Grudge/Waaagh!
Different answers, Striking the Grudge must be used on an attacking or defending unit (notice it specifies target attacking or defending unit, while Waaagh! says each attacking unit, which as I read it sets up a lasting effect for the turn. I can't find anything in the FAQ or rulebook to refute this second interpretation, so you may want to refer it to James for clarification.
these all 3 tactics only refer to attacking or defending as legal target,
so you cannot use that card in the kingdom/quest phase
smalldwarf said:
these all 3 tactics only refer to attacking or defending as legal target,
Only "Striking the Grudge" requires a target. WAAAGH and Grudge Thrower will affect any units meeting their requirements (being attacking) at the time they resolved (and that bonus will carry over until the end of the turn).
So:
1) Striking the Grudge is only playable when there is at least one unit attacking / defending (it may even be played outside the Battlefield Phase, if your opponent attacks you during his Quest phase using "Wolves of the North", for example).
2) WAAAGH! may be played at any time, but only the units attacking at the time it is played will get the bonus, until the end of the turn. Nothing forbids you from playing it for no effect.
3) same as (2) for Grudge Thrower, but only the units attacking or defending at the time it is played will get the bonus, until the end of the turn. Nothing forbids you from using it for no effect (BTW, sacrificing a Dwarf unit is usually a good move if you have some Dwarf Rangers in play 
).
And ?
the bonus cannot be used during the kingdom /quest phase....
your kingdom / quest phase...
So,
ok you can use that tactic in the kingdom/quest phase, but there is no interest....
If you happen to fish Waaagh! from the Orc player's hand with Slaanesh Domination...
1. Do I need to have already declared attacking/defending units to get bonuses from cards like Waaagh!/Striking the grudge/Grudge Thrower. For example, if I use those mentioned cards during my Capitol Phase, or Kingdom, do i get the bonuses?
answer from James Hata
1. No, you do not have to have the units already declared attacking or defending to play the card effect. WAAAGH! and other similar card effects do not actually target the units (as they do not say target in the card effect text). They instead create a continuous effect that waits for the appropriate time to provide the bonus. So, you could WAAAGH! during your capitol phase if you choose to, but the effect would not provide a bonus until you declare attackers.
That mean, if I use Waagh! or Grudge Throwe in my (for example) quest or kingdom or "0" phase, during combat this turn, my units still get the bonus. Hmmm
rasdsaris said:
They instead create a continuous effect that waits for the appropriate time to provide the bonus. So, you could WAAAGH! during your capitol phase if you choose to, but the effect would not provide a bonus until you declare attackers.
Warhammer Invasion definately hold never-seen before game mecanisms. 
Or a really poor wording 
. Those effects should be written as "Until the end of the turn, attacking units gains [P][P]", instead of "Attacking units gains [P][P] until the end of the turn".
OOOoooo tricky, so I was wrong, apologies^^
And more, that could produce modification in the way to play for a few special cases, concerning "waghhh/Wolves of the North" or "waghhh/Wolves of the North/tanquol".
Concerning "grudge thrower", now we can sacrifice "Zhufbar Engineers" before the battlefield phase and that´s nice^^
some other example should exist...
smalldwarf said:
Concerning "grudge thrower", now we can sacrifice "Zhufbar Engineers" before the battlefield phase and that´s nice^^
We could do so since the release of the game, but now, the bonus provided will affect all units, no matter their attacking/defending status at the time you activate the Thrower.
yes, exactly^^
Martin_fr said:
Warhammer Invasion definately hold never-seen before game mecanisms.
Or a really poor wording . Those effects should be written as "Until the end of the turn, attacking units gains [P][P]", instead of "Attacking units gains [P][P] until the end of the turn".
These kinds of effects do exist in other games, and the wording was not too difficult to interpret, when you could compare it to cards like Striking the Grudge which clearly said target attacking or defending unit. When it is a generic phrase about a game state it is probably more correct to assume it is a global effect rather than a poorly worded targeted effect.