Make sure you have a good reason for the check. It will only be accepted to counter vandalism or disruption to Wikimedia wikis. Valid reasons include needing a block of the underlying IP or IP range, disruptive sockpuppetry, vote-stacking, and similar disruption where the technical evidence from running a check would prevent or reduce further disruption.
Be specific in your reasons. Ambiguous or insufficient reasons will cause delays. Explain the disruption and why you believe the accounts are related, ideally using diff links or other evidence.
Make sure there are no local checkusers or policies.
Reason(s): I'm asking here (meta) for a check because the user is a cross-wiki vandal (bs ca el en es et fi fr hu it la lt pl pt sq sv tl tr). A Portuguese sysop has already blocked one of his IPs, the one I'm reporting as first, because it was an open proxy. Unfortunately only one IP of the range 220.127.116.11/18 (AS6939 HURRICANE - Hurricane Electric, Inc., US) was blocked, while lots of other IPs on the same range are still used by him. Furthermore this is not the only range he's using, because the same proxy provides other ranges too, 18.104.22.168/18 and 22.214.171.124/18. All these IPs are being used to make the same edits in different wikis. Such edits are also being done by recently registered users who make almost only these edits, I have no doubt he's the same person, even if I may have missed a few IPs or sockpuppets around the wikis. I have to add one more thing: I'm sorry to have observed that the only real (not hidden by a proxy) IPs he's used belong to Italian IP ranges, such as 126.96.36.199/16 and 188.8.131.52/16, which makes this vandal an Italian, Italian as me. Last but maybe least too, adding such information to the fact that in certain cases those same edits have been done some time ago by an Italian registered user, Ninonino, as shown here and here, and to the fact that this user's last edits were made about one month ago (dec. 4th, 7th and 15th) in the same days the vandal made his, makes me think that this user might be the sockmaster, but since I'm not sure about this last point I'm not including him in the check request. If this is not the right place for a cross-wiki check request, please tell me the most correct place to make it, thank you. Catharinan (talk) 19:00, 9 January 2018 (UTC)
More information for stewards
In this box I'm providing further information about this case, as required by RadiX.
User name list: the limit here is 10 users, so I had to choose to write only the IP ranges (besides the 2 account) I'm sure one person is using. You can find the full list of the single IPs I managed to find here.
In this page list, the first 3 ranges are unmistakable proxy ranges, the last 7 are Northern-Italian IP ranges, "Baka Líte" and "Myeuurn" are accounts created recently, in all these cases the pages edited (cross-wiki) and the edits themselves are identical or very similar.
Here's a pair of examples of admins who blocked those proxies:  (Leon saudanha blocked 184.108.40.206 from 05/12/17 to 05/12/18)  (GeneralizationsAreBad blocked 220.127.116.11/22 from 16/11/17 to 16/02/18). Lately this person is using more normal IPs than proxies, maybe just because in some wikis they're currently blocked. The person is clearly the same: .
Here I'm showing also a few examples of unequivocally inappropriate or disruptive edits sometimes even reverted in pages: . Among all his edits he seem to be obsessed with final accents in Italian names: .
Now I'm naming some pages edited recently by IPs belonging to different IP ranges or accounts and placed in different wikis (I'm not including pages edited by different IPs in one wiki), these pages normally aren't edited daily so that a coincidence would be highly unlikely: Björn Borg, Djavan, Dolcenera, Evolution of the wolf, Mia Martini, Mango (singer), Loredana Errore.
The use of open proxy is forbidden in this entire project (en:Wikipedia:No Open Proxies) as this kind of use of sockpuppets (en:Wikipedia:Sock puppets). The fact that normal IPs are being used to make the same edits in the same pages where proxies and/or socks have been used should prove, in my humble opinion, the relation between the first and the second elements (Wikipedia:If it walks like a duck). In case the proxy ranges and the sock accounts will be blocked, I think that also the normal IP ranges used for the same aim should be blocked or it won't change anything.
Last but maybe least too, as I said 5 days ago, I'm considering another small possibility too: that the user behind the proxies and the socks, the sockmaster, is a Northern-Italian old registred user, Ninonino, and even if I'm not including him in the request I'd like to point out why I'm having a doubt about "him" instead of somebody else. If you watch this user's global contributions you'll notice a lot of similarities with both the pages edited and the edits themselves, including the obsession with accents: Portobuffolé, a page where it seems he tried changing accents in lots of wikis in the past; Mia Martini, art name of Domenica Bertè or Berté (both accents are correct in Italian); Natoli or persons whose surname is Natoli, where both this user and one or more of the IP ranges written above has edited (pt:Natolipt:Antonino Natoli); other pages rarely edited such as pt:Fluxo volumétrico and tl:Io. I'll let you do your considerations about this point, since I'm not sure as I'm about the previous points.
If you need more or more specific information, please ask and I'll provide.
Okay, then "what" should I do to report a user for suspicious socking? Do you understand that we're talking about a a cross-wiki proxy user? And you think the problem is the fact that he's being reported by a no-longer anonymous? Are you sure that it's better ignoring this report because it was done by an anonymous instead of checking the user I've talked about above bringing lots of clues to support my thesis? Catharinan (talk) 20:41, 9 January 2018 (UTC)
Reason(s): Hatake was banned from editing the article Kasem Trebeshina and Alrax1's first edit was on article Kasem Trebeshina. Hatake names references ":0"  and Alrax1 is doing the same thing. Olsi (talk) 22:00, 15 January 2018 (UTC)
The accounts are Unrelated although Alrax1 has a sock - Tin113. Ruslik (talk) 17:33, 16 January 2018 (UTC)
Reason(s): User Vlad Mirsic uses the same pattern of behaviour and tries to initiate the same edit wars. He also uses the same ad hominem “arguments” against the same users. A previous check this month Steward requests/Checkuser/2018-01#Κατακλυσμός @el.wikipedia ) has already confirmed the aforementioned users are the same user's accounts. User Vlad Mirsic created his wikipedia account a few days later. Τζερόνυμο (talk) 08:05, 16 January 2018 (UTC)
Confirmed from a technical point of view. RadiX∞ 17:57, 16 January 2018 (UTC)
Reason(s): User Κουπεμπέ uses the same pattern of behaviour and tries to initiate the same edit wars at the same articles. A previous check one day ago, has confirmed the aforementioned users are the same user's accounts. User Κουπεμπέ created his wikipedia account a little later (hours). Τζερόνυμο (talk) 08:09, 18 January 2018 (UTC)