Cleon
Legend
ok, what you think of the rest of the statblock?
Is it just its humanoid form that is Small? Are the mongoose and hybrid forms the size of a human and its humanoid form the size of a halfling? Not convinced by that, I'd rather it stay the same size in all three of its forms like a Wererat, which is Medium sized in all three of its forms despite a Giant Rat being Small. The old AD&D Giant Weasel was Medium sized, so I prefer Medium Monstrosity (shapechanger).
Just noticed the Skills are both a point too low, it should have Perception +3, Stealth +5 with Proficiency and those ability scores.
Let's see, what else…
Does it really need Pack Tactics? Neither a Wererat or Werewolf (which the beastie is clearly based on) have that trait. If you like the trait I have no objection to leaving it in. Some mustelids (i.e. meerkats) are adept pack hunters after all.
Having both Hypnotic Dancing and War Dance is superfluous, just War Dance would do and I'd tweak the wording a bit.
How about this:
War Dance. As an action, the mongoosewere cavorts and prances, dancing towards a creature within ## feet (the war dance can not affect other mongooseweres). If the creature can see the mongoosewere, it must make a DC 12 Wisdom saving throw or be incapacitated for 1 minute, mesmerised by the mongoosewere's movements. Any other creature within range that see the war dance must make a DC 12 Wisdom saving throw with advantage or be incapacitated for 2 (1d4) rounds. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. The incapacitation also ends if the creature takes damage, or someone uses an action to shake or slap them awake. A war dancing mongoosewere can move up to 30 feet, but must move towards the creature targeted by its dancing.
I'd have the range be greater than the mongoosewere's movement, just so you have the creepy effect of it dancing towards its mesmerised victim for a few rounds. Maybe 90 feet, or three rounds of dancing movement?
I'm also tempted to increase its STR and damage a tad since mongooses are a bit bigger and nastier than rats!
Maybe STR 13 (+1)?
Oh, and all its attacks should have +5 to hit, not +4, due to its DEX bonus of +3.
If you increase the Strength its Shortsword becomes 6 (1d6 + 3) damage.
Finally, a 1d4 dice for the bite seems weirdly low. Maybe 5 (1d8 + 1) instead?