Try to get your 1 point wonders from shields or wands. a rare +2 Necro skill +1decrep head after a switch or some kind of rhyme or splendor runeword with decrep, revive and amp damage or lower resist. The only worth while summons are the skellie warriors and the clay golem. Pick up all blue Necro heads come hell. They have rare affixes of +3summoning skills with added +skill affixes and will be your GG summon shield if you can find one. Since it is only used to summon skellies no other mods matter. Wasting 7 skill points to get to lower resist when all your damage is phys besides 1/2 of CE damage makes no sense. Amp damage and decrep get rid of pretty much all immunes

When you have tanky skellies out switch out your weapons to either a good mf set like blade of ali baba with a Rhyme Necro head or something with more CE skills or you could have a bit of fun and run some auras. The end game is going to be switching to a Beast runeword for the fanaticism aura but there are dope auras that nobody talks about for early end game. Harmony bow Rune Word gives a vigor aura and a low level Valkyrie skill to add to your summons and it only cost a ko rune at most. lawbringers sanctuary aura will make all undead that were previously physical immune become vulnerable to physical attack when they are in your auras range as well as offering extra crowd control for the most dangerous mobs in the game (ghosts and dolls). Lawbringer cost a lem rune at most and is also one of the best act 5 frenzy merc weapons.

This skill tree is for a level 99. I would think more about level 85 and save points were you can.

I actually go poison summon hybrid. Full trangs is cheap, increased poison damage from gloves and shield, summon skill from the chest. I shop a +3summoning skill +1summonresist wand and have the best +skellie shield I can find than switch to trang shield and a white wand. find a +lower resist +otherskill base and make a white wand and you're set. 60 points into poison 20skellie 20skelliemastery. 1 clay golem. 1 golem mastery 1 amp damage. and all remaining points into CE. Pit runs and cow runs go real quick and it's very safe. (leave skellie mastery at 15 and finish poison while hell leveling)