If Sengir Autocrat leaves the battlefield while its first ability is on the stack, its second ability triggers and exiles any Serf tokens that happen to be on the battlefield, and then its first ability resolves and gives you three Serf tokens.
08-06-2016
wotc
Sengir Autocrat’s last ability exiles all Serf tokens, not just the Serf tokens its first ability created.
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