High fantasy book, possibly "Forgotten Realms", including Leviathan-like undead a necromancer creating experimental undeads

Question

I read a book, about a party of adventurers fighting a lich and his armies of undead trying to take over the continent, very high fantasy. It has been a long time (likely between 2000-2012) and details are fuzzy, but it could possibly be in the Forgotten Realms books.

It had a powerful monk like in Dungeons and Dragons , vampires, priests casting spells, colossal Leviathan-like undead that roamed the land, a "mad scientist"-style necromancer creating all kinds of new experimental undead, like higher vampires and other new things not commonly seen in fantasy (perhaps bone golems and creatures make by combining several different corpses together, as well as animal undead). There may have been armies of different fantasy races fighting the undead as well.

Answer 1

This is the Forgotten Realms novel Undead, by Richard Lee Byers, from 2008.

From the Realms Wikia article:

Meanwhile, undead kraken-like behemoths emerged from the ground behind the Council’s legions and proceeded to massacre the southern troops.

That sounds very distinctly similar to what you're describing. There are also a lot of other things mentioned that correspond to elements in the question: a lich overlord, abnormally powerful vampires, giant animal skeletons.