So, in my newest game i'm making in rpg maker 2003(Battle world is the title.) I have so many custom features for fights and storytelling. I needed something for conditions so I added a skill that blocks all meele attacks for 3 turns, I added versions that protect for 1 and 2 turns. I also madde a version for skills. I want to know. Is it a good idea to have these skills or is it a bad idea, making the character OP'ed.

If the skills come at a prince then it should be ok.
For example, if the skills makes you invulnerable to melee for three turns, but you can't do any melee attacks in those three (maybe two) turns either. That way when the player is in a real jam, they can protect themselves from a kind of attack and try to heal themselves, allies, what have you, or cast some spells, but they can't use it to easy-win every battle.

I'm guessing another one of these skills makes you immune to magic for three turns?
In which case, make it so only the melee or the magic can be on at a time, but not both, and make sure you have a variety of enemies. This adds an element of strategy.

Basically, it's ok to have your characters as resourceful as you like, so long as the game still has some difficulty to it.

I think it's a great idea if there is a trade-off, like Sparrowsmith said. 3 turns seems like a lot though - you could easily keep recasting the spell on all your party members and never get hit. I'd make it so that you could only use the ability once per battle or something like that.

Also, instead of making it turned based, you could make it so that it lasts until you get hit by whatever it defends against, like the nul-element spells in FFX (i.e., nul-ice stays in effect on a character until they are hit by ice. They don't take any damage but the defense immediately goes away).

Honestly, if my characters wouldn't be able to attack while they were under the effects of that spell, I likely wouldn't use it unless I just need time to heal.

I think Shin Megami Tensei: Nocturne and Digital Devil Saga did it really well. There were abilities that allowed protection from a certain element. If an enemy used a spell that you were protected against, the enemy would lose a turn. The same would happen for the player. Attack a monster that's immune to ice with an ice spell, you lose a turn. Along with that, though, was the fact that exploiting a weakness gave an extra turn. So, as the player, you'd want to protect against the enemy gaining an extra turn, so you'd use the protection spell. The trade off was the fact that forgetting to cast the spell could mean the difference between victory and defeat, even in a random battle.

I say that if you want to use spells like that, they need to be really useful, otherwise I doubt the player will use them. For instance 'Haste" in most Final Fantasies is a waste of a spell. It doesn't grant that much of an advantage, or rather, the advantage is negligible when you can win just as easily without using the spell.

So if you can work it into the fundamental battle strategy, I'd say go for it. But if it's just something "useful" the player could do, I wouldn't bother.

It sounds OP with me. I agree with rewells.
In MMOs they put cooldowns on your more powerful skills, thats one way you can balance it here, have it only once per battle or casting it will start a 10 turn cooldown.

I think 3 turns is a lot, but it depends on what kinds of attacks your enemies have, the AI is not that smartest and if they have magic but cast melee attacks for 3 turns it makes the spell even more OP.

In addition it matters what kind of encounters you have, if you can clear trash enemies in 2-4 hits, having a 3 turn immune is a lot. But if your battles are really tough where even random enemies take 5 minutes to kill, then 3 turns wont be a long time.

Nul is also a very good option, have it absorb an attack.

Greatly disagree, giving options is a good idea, it allows players to come up with their own battle strategies. I, for example, use haste quite extensively in games because I value being able to speed up a victory, even though it'd takes the same number of turns, one more even since I had to cast it in the first place, but overall its a faster battle, that is my play style that couldn't happen without that choice.

In terms of protection spells I rarely use them, but if I had that one you're proposing in my arsenal, yeah I would. But only because, like others have said, its overpowered. You'd be a fool not to use it really. And that's the trap, its so powerful a move you would have to use it, you just would. It would become 'fundamental' as Ennaya puts it. Really, I think number of turns is the wrong variable for this.
Think of Pokemon, the protect skills on there are only for one turn. The absolute opposite so it must be right, right? Wrong. They are absolutely useless unless the enemy's using a two-turn attack that requires powering up on the first turn. If its used at any other time then all it accomplishes is stalling, because no-ones harming anyone.
So what are your options?
Well I'd go with one that caused a continual mp drain to maintain (differs from a oneturn defence because you'd still be able to use other attacks).
One that massively reduced other stats (if it continues to be a three turn affair).
You could even go Yojimbo with it and have a shield that cost money to maintain (something I always find interesting as money rarely features in battles).