I don't think there is any resource other than merely making new characters and reading the skills.

Necros no longer have summons, they have a death knight which is a strong unit that has an aura. They can summon all golems at once, and the golems have been adjusted slightly. Also, bone armor acts as a super buff mastery skill when wielding wands, and wands have had damage buffed.

In terms of the other skills, lots have been altered and changed:
-Cold mastery is +% damage.
-Static is a screen wide nova that does less damage.
-Tons of synergy changes
-Zon passives have been changed
-Can summon both shadows on the sin tree

More, just too lazy to list them all, plus I probably don't remember then. I haven't seen a skill planner, but it's not hard to use a trainer and see how well the skills work in single player.

he means no revives.

There really were a ton of changes made in HU; your best bet to know what you're doing without messing up your build is to post beforehand any questions you have on a specific character--or test in single player first.

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-ISO- Moonstone Rubies, +6/-6 Psn/Lite Facets,
Hearts (pal/nec/dru/zon), Braaaains

or just make a character and mess it up - and then make another.

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People who live in cinder block houses can throw whatever they want.

This

Zonfire + Udietoo are your best friends for testing gear and skill builds without wasting the time leveling a character and breaking it. I have ~18 single player characters, and only actually play maybe 6 of them - the rest are test characters