OK, so in Part 1, we tackled army special rules and magic items. The items were greatly underwhelming, the special rules were cool. So now let's do a look at the Lores of Magic for the little green skins.
First a word on OnG magic. There is no Teclis here. No Supreme Sorceress with Power of Darkness. No Dual Slann insanity. Orc or Goblin Shamans will never dominate the magic phase, and thus, you shouldn't base any of your plans around magic. Consider any offensive spells your successfully cast as an unplanned bonus in your gameplan.
Little Waagh Magic
Lore Attribute: Sneaky Stealing. Whenever you gobbo successfully casts a spell, on a 5+ you steal a dispel dice from your opponent and add it to your power pool.
This is pretty cool. It creates an obvious strategy of casting your Little Waagh spells first to draw out dispel dice one way or the other, and then drop the bigger spells later in the phase. To make this work, you need a L4 Orc shaman and lots of low level goblin shamans, which is thankfully not too hard to do.
0 Sneaky Stabbing 6+. Grants armor piercing to all a unit's attacks. If that unit is fighting in the flanks it re-rolls all to hit and to wounds.
This has good synergy with Magic Mushrooms. Throw 1 dice at it, getting a freebie with the shrooms and you have an easy way to use Sneaky Stealing and get a respectable buff to your units. It's pretty good, especially in an army with Spider Riders, who are suited to getting flank charges off.
1 Vindictive Glare 5+. 24" magic missile that does 2d6 str 3 hits. Can be buffed to 3d6.
Yawner. OnG don't need magic missiles, they have warmachines.
2 Gift of the Spider God 8+. Short range augment spell that gives a unit Poisoned Attacks.
Somewhat high casting cost, but the ability to give shooty goblins poisoned attacks is strong. Especially if they already have armor piercing, too.
3 Itchy Nuisance 8+. Hex that debuffs an enemy unit's Movement and Initiative by a d6.
Wow. Now this is a strong spell. This is how you kill deathstars. Every turn their movement is -d6 is another turn of war machines pounding the crap out of them. When you do get to combat, they will likely be I1, which means your Orcs will actually strike before them. This is golden.
4 Gork'll fix it 8+. Hex that makes target unit re-roll all 6's when rolling to hit, to wound and armor saves.
This isn't bad, but it's not great. It's best used defensively against a shooting unit like a big Skink or Gnoblar (or Goblin!) horde to mitigate their shooting, since they will usually need 6's to hit anyway. Even works well against DE crossbowmen who typically need 5+ to hit.
5 Night Shroud 9+. The shaman's unit gets softcover against shooting, and anyone charging them has to make dangerous terrain tests. Can be buffed to 15+ to affect every unit within 12".
The dangerous terrain part is the cool part. This is your anti-horde defense, as if an army based around warmachines needed more. 40 Marauders charge you? Well, odds are that 6-7 of them will go poof before they get to swing. Not shabby, but not exactly Final Transmutation, either.
6 Curse of da Bad Moon 15+. Makes a small template that moves 4d6 inches. Any model passed over by the template must make a random characteristic test or die. Can be buffed to 25+ for a big template and allows the shaman pick the characteristic to test on.
Green Sun of Xerus? This is definitely powerful. Powerful enough to consider taking a Power Scroll on a level 2 shaman who picks spells after the L4 rolls. This is potentially more devastating than Purple Sun, in that it can hurt Elves and WoC, which the Purple Sun doesn't scare too badly. Seriously though, as powerful as this can be potentially, you'd be foolish to make a game plan based around getting it off. Too much bad stuff can potentially happen, and it requires a substantial investment in a Lord level goblin shaman which is a mistake.
Summary. Well the Lore has some interesting stuff. The strength of the Lore is spamming easy to cast small spells to drain the opponent's dispel pool. Itchy Nuisance and Sneaky Stabbing are the two all-stars in the Lore. The ultimate spell is a game changer, but unreliable. Stick to using Sneaky Stabbing to do some Sneaky Stealing, and you're on the right track.