tConfig Version of Hydrolyth (Ever Ice)
Ever Ice Bars are crafted from 4 Ever Ice which you can obtain from Comets in the tConfig version. In the source mod, this bar is replaced by the Hydrolyth Bar, also obtained from Hydrolyth ore from Comets. The crating recipe in the source mod is 5 Hydrolyth Ore and 1 Solarium Ore.
Ever Ice Bars are used for many things, but most predominantly the Ever Frost Armor, probably the best ranger armor.
Source Mod Version of Ever Ice/Hydrolyth
In the source mod, Ever Ice is named Hydrolyth. It can be found as ore at comets and can be made into bars at a Caesium Forge. Hydrolyth bars play a crucial part in Superhardmode gear, namely the Berserker Nightmare, Superhardmode Bars, and the Milotic summoner armor set. Hydrolyth is the same thing as Ever Ice, but used in different crafting recipes, and can be found from comets just like Ever Ice.