Here are some clarifications of the Veto rules personally corrected and confirmed by the game designer Wolfgang Kramer:
*9. Veto: If you have taken this card, then lay it in front of you
where the other players can see it. You may use it to veto any one
special action that a player wishes to carry out either during the
remainder of the current round or during the next round. You may only
veto a special action, the normal placement of Caballeros is carried
out as usual. You may only use your Veto once, and during the special
action is carrying out. You may not cancel an action once carried out.
Once you have used your Veto you must return the card to the box, if
you have not used your Veto by the end of the round after the one in
which you took the card, then you must give it up.
The opponents can ask for or come to an agreement with you about what
they can do. * An opponent wants move some Caballeros, he can ask :
"If I move this Caballeros from ... to ..., you play the Veto card?"
or "May I move this Caballero, and this else?" or other similar
If an opponent doesn't want to carry out the special action, you can't
force him thanks to the Veto, because it can prevent (but can't force)
9.1. Veto & Special action addressed to only one player:
The player who is on turn determines the order of the steps of a
special action (rule 4), so the Veto can stop his special action at
any time before it ends.
- "INTRIGANT:4 BELIEBIGE CABALLEROS AUF DEM SPIELPLAN BELIEBIG
UMSETZEN: The player may remove up to 4 Caballeros (their own and/or
opponent's) from the board, and replace them in another region or in
the Castillo.": A player may move four Caballeros. He has already
moved two. You were pleased with these moves. Now he plans to move one
more. You don't like that, so you play your Veto and he can't execute
the remainder of the special action.
There's more where this came from, but I thought I'd stop there! I think this illustrates the power of Veto quite nicely: you can indeed find out what a player plans to do with their move before choosing to veto it; and you can even use the Veto partway through a move if it begins to take a direction you don't like!