The Importance of Cast Level
The topic of cast level is something which isn't covered much in or outside of Alter. For a caster there is nothing as important as their cast level. This determines everything about your character's abilities. Not only with active attacks, but also with the strength of passive spells and skills. For this reason you really need to focus on gathering as much equipment which is plus cast level as possible.
The way cast level works is like adding levels to your character. As you level up, your spells become stronger with your character's main level. Take necro for example. If you cast spectral claw at level 30, then it has the strength of level 30. If you are a level 35 necro and cast spectral claw, then it is five levels stronger and will do a little bit more damage. Now if you add cast level to this you can add a very noticeable amount of damage boost to not only spectral claw, but all spells. If you wear something on armor and jewelry slot that is +1 in cast level, and also +2 for your wielded weapon you can add 17 levels to the strength of your spells. So casting that spectral claw at level 30 with full cast level gear means you are actually casting a level 47 spectral claw. This means that the max level something can be cast at is level 56, level 39+17, and I'm sure map builders keep this in mind when making all maps. If a place is level 30, then they are expecting that a caster will be casting at level 47 on that map. If you aren't using a full set of cast gear, then you are putting yourself at a severe disadvantage. For this reason you want to make sure you are always wearing equipment that is +1 for your class, and +2 for your wielded.
Always wearing equipment that has a cast level means you may not have all the stats you want, but it ends up being worth it in the end. You may have less mana regen, but you will be doing much more damage. This means fights will take less time, and you'll actually be casting less than if you just stocked up on mana regen equipment with no cast. It can be tricky to find equipment that's all plus one, but there are some handy lists here on BSG with where to get each piece for your class. We don't show you exactly how to get it, but rather what map the equipment is on. It is a helpful nudge in the right direction, but one which still allows you to find the stuff on your own.
Necro Cast vs Druid Cast
The two main minion classes in game are necro and druid, but the way they handle minions and cast is quite different. With both classes the cast level determines the strength of the minions, but with necro you cannot remove any of your equipment with cast level. If you do your minions instantly drop in HP and damage. This is not the case with druid however. You can wear druid cast then switch to a different equipment set, and all your minions will be just as tough. If you were to do this as a necro your minions would become quite weak. This is why it is difficult to use necro as anything except for first or sixth class, but druid can be used as a secondary class and work out pretty good.
Skill level with Warrior and Thief
Skill level is pretty straight forward when it comes to thief, at least it seems to be. The higher the skill level the better all your thief stuff is. This includes offensive attacks, and also things like sneaking, hiding, and stealing. The chance of a freak backstab is increased with your skill level, and it seems to give a hidden boost to hit roll, one that doesn't show up anywhere but somewhere in the deep dark back end of the game. You want a good amount of DR and hr to go with your thief skill, this ensures the most amount of damage possible for those backstabs and other attacks. Like with a caster, I think most thieves shoot for a full set of skill gear to ensure they do the most damage possible, while taking the least amount possible.
In my personal experience warrior is a bit different than the casting classes and thief. It is good to have war skill, but it doesn't seem to be the deal breaker it is for other classes at lower levels. I went through the first three islands just focusing on crafted equipment with DR and armor class, and everything went pretty good. After getting onto the mainland war skill is quite important however. Warrior equipment is about as good as mage, meaning it is pretty horrible. Everything with warrior is based on damage, but it is hard to find equipment with both war skill and DR. This starts to change from level 31 to 35, but up until then it really blows.
Like with thief your war skill is going to give you a hidden boost to your warrior attacks. This is probably the case for all attacks, but most people only talk about it in relation to the big power attacks like ground strike and leap. It seems to also give a very nice boost to your passive skills like parry which is always good. What I've been told is you can expect a hidden extra DR for warrior attacks from war skill, but how true this is, I cannot actually say. You do more damage when wearing warrior skill equipment with DR though, so some part of it must be true. If someone corrects me at a later date I will be happy to change this to reflect the proper information. This is the issue with effects being hidden.
Get yourself equipment that all has cast level or skill level. The game is made assuming you will be wearing equipment to boost your cast or skill by 17, if you don't do this every map is going to be way too difficult. It is frustrating this isn't pointed out and stressed anywhere in game.
You should also be aware that having a piece of equipment with a negative cast level can make it so you cannot cast spells. For example if you are a warrior cleric with a set of leg armor with a negative cleric cast level on it. This means your cleric level is actually minus one. So if you wish to cast major heal when level 23 cleric, while wearing the negative cast legs you are actually level 22 and the spell will fail almost every time. This happened to me, and I was told by an admin it was self explanatory why it was happening, even though new players are not told about cast level, or the importance of it. You can always check your cast level with the show cast command.