As in spanish is not really that clear, in english this card reads while attacking so, can it be used at any time during the attack? for example after opponent resolves some modifications on his defense result?
Timing for Lock On
Because Lock On adds or removes symbols or accuracy, it must be used during or before the 4. Apply Modifiers step.
If the defender has abilities that trigger simultaneously (Apply Modifiers), the mission/core rules/abilities are applied first (weakened, hidden), the attacker resolves his, then the defender.
Edited by a1bertNever thought about this one before, so if attacker plays lock on and defender has cower or similar, defender could re roll?
If he did so presumably if he rolled another x it's still be discounted but a surge cancel and block might save him
No, rerolls are step 3.
Almost all "while attacking" or "while defending" abilities have a certain step to trigger them in (see RRG page 6). Fenn's Havoc Shot is one of the few that can actually be triggered at any point of the attack.
See the following link for a list of most attack-defense-related abilities in the campaign. There are alot.
I love asking the guy with the Dodge result if he wants to reroll. They always laugh and say no, then I play Lock On to kill their figure.