Leudigar sits down to rest, as the party gathers around the imposing statue of Akbar...
At this point, it's worthwhile noting that M&T p3 specifies: Medusae: Number Appearing: 1--4.
Since it is generally thought that M&T's Number Appearing stats are intended for outdoor encounters only, DD4 "hacks it" into explicit numbers encountered, and numbers in lair. I.e., the DD4 Compendium p86 has Medusae: Number Appearing 1--4, and Number in Lair 1--4.
However, DD5 (and hence our current Hinterlands play) uses a more "correct" procedure for determining the number of monsters encountered underground, per U&WA p11--12.
This is reflected in DD5 book2 WIP 20170320 p4, which shows Medusae as a Table IV monster, and p10 which shows that one Table IV monster occurs on dungeon levels 1 thru 4. Importantly, 4--6 players will bring double the basic number of monsters shown on p10. Therefore, a party of six players will attract two Table IV monsters on dungeon levels 1 thru 4.
Be aware that your dutiful referee chooses interpret the fixed "2 monsters" as implying the possibility of 1--3 monsters (yielding the required average of "2 monsters")...
the Elf Medium (MV 12", AC 9, HD 1, hp 1/1, AL N) great cloak, lantern
; spells: color spray; scrolls: sleep, sleep, charm person
Hirelings: Georges; torch