So i've tried to do as much of my own research as possible but i found nothing concrete.
We all know Italy wanted to annex Dalmatia which meant having to dismantle Yugoslavia, so Italy did have a very anti-Croat perspective barring that they wanted to annex and Italicize Dalmatia and Istria, which also meant a very anti-Slovene ideology (They had concentration camps for Croats and Slovenes as far as i know)
But what did Mussolini and in turn the wider Italian Fascist party think of Croats outside of Dalmatia? Croats in Slavonia and Bosnia, places that i assume Italy wanted in their sphere, did they consider them a people worth allying to or a menace to be eradicated?
Continuing on to the second part of the question, much like Dalmatia Italy wanted to annex Albania and some surrounding regions. Were the Italian Fascists anti-Serb and sought to cleanse Albania, who's borders would be expanded OTL of Serbs? Or did Italians see Serbs in a friendly view thanks to allyship in WW1. And did Italians defend Serbs from Ustashe and Albanians during WW2? I heard that sometimes Italians stepped in because they were extremely brutal against the Serbs.
And for the final part, Did Italy have any aspirations to puppet Serbia or put it in their sphere of influence? Did Italy have any post-war plans for Serbia or was Serbia to become a German client-state.
Italy was a staunch enemy of Yugoslavia as a whole. Not only did Yugoslavia thwart Italian ambitions on Eastern Adriatic, it also presented a threat: it had potential to turn into a serious rival of Italy. Italy had, as far as I know, no clear strategy in that matter, but the goals were to take over the littoral and eventually turn Yugoslavia (whole or dismantled) into a sort of a client state.
In the Interwar Period, Italy was the biggest enemy of the Yugoslav state. It defeated Yugoslav ambitions to control Albania; it managed to keep Vatican and Yugoslav governments from reaching any real compromise (resulting in a Kulturkampf of a sort and incitement of anti-Yugoslav sentiments among Roman Catholics); it hosted and trained various anti-Yugoslav factions (most prominent of them being the UstaĊĦe); in 30's, Italy created a network of anti-Yugoslav alliances with Hungary, Bulgaria and Albania; it organized joint Bulgarian-Albanian cooperation in order to occupy Kosovo-Metohija and Macedonia; it forced various concessions on the sea and even in the littoral from Yugoslav governments.
Now, one may be inclined to think that due to their maritime ambition, Italian administrations did not want any trouble with rest of the Yugoslav territories/population. However, one must understand that both Croats and Serbs did not want to surrender littoral. Both of these nations had (and still largely have) kinsmen on their very coasts (for Croats it's obvious, for Serbs - Montenegro had a clear Serb character, there were Serbs on the Croatian coast as well, and there was even a small Serb (Roman) Catholic movement in Dubrovnik and surrounding areas. Any move that fortified Italian positions on the sea and in the littoral was met with huge uproar and bloody demonstration in both Zagreb and Belgrade. One should not forget that Yugoslav solidarity did exist back then.