Can Killer Instinct be used with a charmed pet? And if so, would it be possible to charm a Puk, use Killer Instinct and give everyone in range Demon Killer?
Falkirk might have some ideas, but I have struck out several times trying to test this.
First, you need a zone where both charmable Puks and Demons exist. I tried Abyssea-Vunkerl and apparently abyssea monsters are immune to charm. Ended up going to Escha-Zitah (This is the only zone I could find where both Puks + demons exist, but lmk if I missed one and I can try again). Had to remove my 3 Killer Effects Vorseals (because Trusts get them too), then re-zoned, and then summoned two tank trusts. Went to Escha-2, charmed a Puk, then went to 6 south and popped Revetaur, a Tauros (demon) NM. Engaged and let AAEV/Valaineral take hate, then disengaged. Killer effects are nerfed vs NMs (10%), so it's possible that it just never procced, but for the entire 3~minutes Revetaur was wailing on them, I didn't see one intimidation effect. Wanted to be sure so I repeated the process and never saw an intimidation for the entire duration (didn't bring Relic helm).
Went to test if charmed pets' can activate Killer instinct at all, so I went and grabbed a monkey, then popped Killer instinct, went to fight a Tarichuk (lizard) and let trusts hold it for a few moments. Got several intimidations in a few seconds, so it does work with charmed pets. So unless something in particular is going on with Revetaur NM (like maybe Tauri areimmune to intimidation, idk), I think it's more than likely that the killer effects gained from killer instinct bonus only applies to Ecosystems 1&2.
By the way, charmed pets immediately despawn in Escha when you pop a Gaes Fete (Confrontation effect). Also, I managed to charm pets in Escha but then had to hop on a call, bathroom, do work etc, looked back at my computer and noticed almost a 30 minutes later the monster was still charmed. Didn't use Familiar. Don't ever recall normal monsters staying charmed for that long, and I didn't wear any specific Charm+ gear.