Spells of Ruin
You really can't go wrong with the Spells of Ruin. All of the spells are powerful in there own right and you'll rarely run into a situation in which you end up with a useless spell, but they're not all always useful. For example Howling Warpgale isn't any good against armies without shooting but wrecks Wood Elves and Dwarfs and Cracks Call isn't so great against any of the elves but annihilates Orcs and Goblins, Dwarfs, Undead and anything else with low initiative. In situations where you get a spell you don't need, just swap them out for the Dreaded 13th or Warp Lightning for your Grey Seers and Warlock Engineers respectively!
Skitterleap is a pretty powerful spell really. It has some solid synergy with some of our more powerful items like the Doomrocket by Skitterleaping an Engineer on the flank of an army, it lets your characters disappear from combat if it's too dangerous or you can use it to cause serious issues with their movement phase with Warlock Engineers that you no longer need. You can use Engineers in this manner in basically the same way an elf player uses Great Eagles: place him on an angle an inch away from the unit so they have to charge him. Sacrifice the useless! Such is the Skaven way.
I'd almost never swap out Skitterleap unless I absolutely needed other spells, but that's not often. For only a 5+ to cast, it's just too good.
2. Warp Lightning
People take level 1 Warlock Engineers just for this spell. Warp-energy Condensor makes it even more powerful. It's incredible for removing chaff, light cavalry, hitting lone characters or models, and just in general causing some damage. An all-round good spell with a low casting value.
3. Howling Warpgale
One of the more situational spells, as mentioned. If you find yourself against any kind of missile-based gunline, it can be well worth it. Otherwise it's probably better swapped out for the 13th or Warp Lightning.
4. Death Frenzy
Turns Slaves into killing machines when you need to. Clanrats and Stormvermin too. Really, a nice spell to have, but not always as fantastic as other spells. If you don't see yourself using it during the game, just swap it out.
Another damage spell, and a pretty interesting one at that. It's nearly double the casting cost of Warp Lightning and has one less strength, but it will hit more guys, doesn't hurt you on the roll of a one, has Flaming and causes a Panic Test if they take a single wound. I definitely think it's worth it. The main thing to remember with this one is that it [i]does not scatter[/i] because it says [i]place[/i] the template anywhere within 24". That's what really makes it good.
6. Cracks Call
A very powerful spell against low Initiative armies and units, and especially dangerous to War Machines. I'd even keep it over Howling Warpgale against High Elves (but not Wood Elves or Dark Elves; their shooting is far more powerful than High Elf shooting) for the chance you might snipe a character with it. It's also ridiculously powerful against Ogres. And when combined with Skitterleap. And especially when combined with Skitterleap against Ogres...
Spells of Plague
I'm going to be honest with you: the only reason Spells of Plague is even worth considering is because of Wither and Plague. Most of the spells are trash, but those two are so incredibly powerful it still makes it worth trying. It's a gamble, but it pays off when you get one or both of those spells.
1. Pestilent Breath
Meh. No armour allowed makes is nice, and it is cheap and has the potential to hit a bunch of guys, but it's nowhere near as flexible or powerful as Skitterleap and other similarly costed spells. Nice with Wither, though, especially being only S2.
2. Bless With Filth
The third best spell in the lore in my opinion, and the second cheapest to cast. Poisoned Attacks can really help your weak Skaven get some more wounds on. Very nasty against monsters. Especially if you manage to get Skavenslaves into them.
Probably the most subtly over-powered spell in the game. Dropping a big unit of High Elf Spearmen to T2 is just plain nasty. Ogre's only real survivability comes from their Toughness, but hit them with Wither and suddenly they're as easy to wound as Clanrats. It's a mean spell and not one to be underestimated.
This is my least favourite spell in the game, to be quite honest. 3D6 hits is nice, for sure, and you can hit a good number of units, but they don't ignore armour and the damage really ends up being very negligible when all is said and done. At least Pestilent Breath goes straight through 2+ armour saves. Not worth casting over other spells really.
5. Cloud of Corruption
A reasonable spell for a Plague Priest to have, seeing as he's the only Wizard you want that close that has access to the Spells of Plague. Skaven are meant to die. Get used to it. Just remember that every model of theirs is worth at least 2-3 of yours, if not more, so losing a few of your own guys for some of theirs is always a worthy trade.
A very, very powerful damage spell. Like, incredible. I'd put it second only to the Dreaded 13th in terms of the damage it can cause. The spell can backfire, but as long as you're thinking the way a Skaven general should, you won't care!
I cast Wither on a unit of Dwarf Great Beards, then hit them with Plague in the same phase. Over half of the 30 models in the unit went down, the spell then bounced to a nearby Organ Gun and scored a wound, then it bounced to another Organ Gun and caused a wound, then a Cannon and also caused a wound, before finally hitting my own unit of 20-odd Clanrats with Warlord and Plague Priest, bringing the entire unit down to 3 Clanrats, the Warlord and a wounded Plague Priest. Needless to say, I've never had a more successful magic phase!
The Dreaded Thirteenth Spell
Time for more honesty I think, which is quite hard for me, being the mighty Skaven general that I am, but here goes: the Dreaded 13th is OP. Get used to it. In fact, love it. I do. Don't like having incredibly powerful spells? Maybe you're better suited to Ogres, because you're clearly not thinking like a rat.
Anyway, there's really no subtle tactics with this. We go from sneaky one-dicing Skitterleap for some cool movement tricks of setting up bombs, to just pointing at something, throwing 6 dice at the table, removing the previously pointed at unit and placing some more Clanrats that can kill stuff and offer up no Victory Points to the enemy.
A few tips:
- Small, expensive units (Chaos Chosen, Swordmasters, Wardancers, Grave Guard) are the best target for the Dreaded 13th
- The Clanrats from the Dreaded 13th offer no Victory Points to the opponent and are essentially worthless, treat them as such (i.e. throw them at things to keep them away from your Grey Seer, use them to redirect, anything is viable)
- The Clanrats from the Dreaded 13th can be given any kit, so always place a unit with Shields and Full Command
- Take the Dreaded 13th on your Grey Seer every single game unless facing Ogres. Nothing is as valuable.