Sleen: Their bodies resemble that of a snakes with the top half being that of a spider. The Sleen are among the few entities that resemble things that already live on the planet.
Size estimates place them at 20-40 feet long and 5 foot wide including the front legs. They seem to gravitate towards cramped places were the can barely fit.
Though they have been seen amongst the Entities that have come out from the United States Breaches it seems that Australia seems to get more of them.
From the little information we've gotten from the Australian department assigned to dealing with their Breaches Sleen seem to be their most common entity.
Reports from China, Russia, Spain, Turkey, Indian, and South America all seem to put them as uncommon creatures. Though as previous investigations have shown the reports they've shared with use can be unreliable.
Sleen seem to actively hunt, despite their massive size they are agile and able to chase at high speeds.
Liquidation Team Z11 reported that during the 2008 Florida Breach that Sleen was able to keep up with a armored Humvee going at full speed. Other accounts including ones from Wyoming 2018, South Carolina 2003, New York 1999 have also corroborated that fact.