TL;DR: When skeletons encounter water they take damage. During the day they will actively seek water sources or shade when exposed to the sunlight.
What this mod seeks to accomplish is to mitigate the rage inducing situations where you spot that precious ore, or are out for a stroll, when a horrible no good skeleton appears and ruins your day. You try valiantly to swim to meet the beastie head on in honorable combat but Sire Skellington wants nothing of it. Instead of being fair and engaging you in honorable melee combat the skeleton rains down the arrows upon you! You struggle with your sword but no avail! Skeleton knocks you back, laughs at your misery, and steals your epic treasures when you inevitably meet your demise.
A little more:
This should work with any skeleton mob that is of the entity type skeleton. I make no promises for this being the case, nor for mod compatibility. The skeletons do not die instantly.
This mod is provided as is. Always do a backup before installing new mods. No warranties, support, or otherwise is explicitly granted. Mod author is in no way associated with Minecraft, Mojang AB, or Microsoft.