Must be
multiple countries from the Arab League or the peninsula
not already in major active conflict with Israel (i.e. this precludes only Palestine)
using official forces or forces acting with official permission
working together (can join other Arab states other than Palestine already in conflict to qualify)
either attacking first, or attacking after Israel pre-emptively strikes against any gathering of forces (if Israel instead attacks, say, primarily civilian targets, then Israel is the aggressor against that country for the purposes of this question)
(feel free to suggest more criteria if this doesn't feel sufficiently clear. will lean on spirit of the question in the meantime, and in general)
Between houthis and Hezbollah's fairly consistent bombing (the de facto powers controlling Yemen and Lebanon in practice) I'm not sure this shouldn't already settle as yes.
this question was affected by the bug over the weekend that prevented subsidy getting added, which is why it feels so swingy. I've added a small bit back in so it's not completely terrible to trade in.
Actually, the most likely candidates are countries border with Israel. Egypt and Jordan has peace agreements and rely on American support. Syria and Lebanon and in fragile position politically and economically. So Iraq?
Would this include a coalition of terror groups, ie. Hamas, Hezbollah, Syrian/Iranian Rebels (IS/ISIS/ISIL), Wagner team up against Israel or would it need to be more like Syria and Iran as a country create a coalition and attacks?
@SirCryptomind "coalition" to me says it must include multiple national forces, regardless of other members. seems fair?
@Stralor What about if Lebanon & Hezbollah attack Israel while Israel is attacking Gaza? (They are already fighting, but more like "hey, you stay on your side, we will stay on ours" but it could escalate.
Say, for example purpose: Those 2 attack in response to: Israeli strike kills a Hezbollah commander in Lebanon (Reuters)
Would that count?
And for that. do you consider Lebanon an Arab country since they are a Member State of the Arab League?

Last question is, does the initial aggressor matter?
@SirCryptomind ooo good questions.
Lebanon: yes. counts, but only if official (not if Hezbollah acts independently), and also not enough on its own (not a "coalition" of Arab states)
Palestine: does not count as we need new countries
Initial Aggressor: hmm, yeah I think that matters. Israel could "pre-act" against them building forces to attack and I'd still count it though