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): Μαυρο Μαργαριταρι exhibits the same editing pattern of blind reverts and silly vandalism as Μαδαρός in the elwiki article on the battle of Crete
(el:Μάχη της Κρήτης -- please check the article's history page). The former is an account that was activated and started editing the article only a short while after the latter was blocked indefinitely as a sockpuppet. There may well be a number of sleepers, as the sockmaster (Vrahomarinaner, whose account has also been indefinitely blocked) tends to edit WP using a large number of accounts (as previously confirmed after CU requests here) or as an IP. Ασμοδαίος (talk) 18:44, 18 March 2018 (UTC)
comment: I have added a sleeper (user "Επισκεπτήριος") who woke up a few days ago. --Firestarterfighter (talk) 18:40, 21 March 2018 (UTC)
Oppose There is no need for further check for vrahomariner. The greek comunity is against identity phishing. Please don't response. --Υπάρχω (talk) 20:57, 22 March 2018 (UTC)
Reason(s): User:Hatake (master) is a prolific sock creator in the Albanian wikipedia (sqwiki). Ever since he was blocked in January he has been creating one sockpuppet after another. As soon as his latest socks User:Flladitja,User:Ch'hilli and user:Llazgo were discovered and blocked, after a checkuser request here, we suspect that he created a new sockpuppet called user:Milonjë. This new user seems experienced and in a short time he has edited a lot of articles Hatake edited See this report--Udha (talk) 15:21, 20 March 2018 (UTC)