FitzTheRuke
Legend
Good to know. That's what I thought, but it's been awhile since I've seen this somewhat rare occasion. I'm definitely the type of DM who is not going to nit-pick on word choices. Invisibilty is not an attack, but Lionel could probably barely tell the difference. I think I once used the ready action as a halfling rogue with the trigger, "If he wiggles'is nose or wha-e'er they do when they're a' castin', I'm gonna shoot'im!"@Prickly Pear
Readied actions take place after the trigger event. So, If you say, "I ready to shoot if the wizard attacks" (and if @FitzTheRuke allows your trigger to go off even though wizard didn't technically attack - although, you could have just as easily designated 'if the wizard casts a spell' so it feels like semantics to me), you have to attack after the spell is cast - so he'd be invisible when the attack happens.
Edit: But since Escella counterspelled the spell, he never actually went invisible, so your attack goes off without a hitch.
Insightful Fighting will certainly recognize that a wizard is about to cast, and is vulnerable. At any rate, yeah. Escella countered the invisibilty before it went off (based on the fluff we've used for her, magical abilities, she probably doesn't even quite know how she's doing it - more like she "feels" the magic he's gathering around him, and "steals" it/throws it away.)