I was watching the Fate/Stay Night OVA's, when a thought flashed past my mind. Quick as I could, I opened my notepad and began furiously typing. This is the result...(It's still very incomplete although!)
I see numerous problems.
First of all, I'm not sure the whole master+summon thing is properly thought out. How powerful are they compared to each other? What's to prevent the squishier one from being focused down by both members of the opposing team? Also, doubling the number of rolls you need to do might add up quicker than you'd think.
Servant Archer
Health: For those with Strength as their main attirubte, a 1d40 is rolled, minimum is 10. For those with Strength as their weakness, a 1d15 is rolled, minimum 5. If neutral, a 1d20 is rolled, minimum 8.
This irks me because it's roundabout. Why not just roll 1d31+9 or something? Also, I hope you realize how utterly random these results will be- the minimum and maximum values are equally likely, so seeing one Str Servant with 10 HP and another with 40 right out the gate wouldn't be surprising. More on this later.
There's also a pretty massive difference between an attribute being their strength and not their strength, but not so much between being normal and a weakness. I'm not sure I disapprove of that, to be honest.
Mana: For those with Intelligence as their main attribute, a 1d30 is rolled, minimum is 15. As their weakness, a 1d10 is rolled, minimum 3. As neutral, a 1d15 is rolled, minimum 6. NOTE: Mana will be regenerated by 1 point for every 20 points max every turn. So if your serant has 25 Mana, then they'll regenerate one Mana per turn. The minimum is one, so even if you have only 15 Mana max, you'll still regenerate One every turn.
The main attribute method fills me with rage. "If Int is your main attribute, I roll a die. Half of the time, this result will be below the minimum and I'll have to reroll." Just add it as a bonus or something- unless you've explicitly got a physical d30 that you've been dying to use, there's zero reason for these shenanigans.
Then there's mana. I don't like how mana's shaping up, for two reasons. One, the regen rate seems too low- it's
probably better than nothing, but you're still looking at your classic "casters burn through all their mana and then hit things with a stick if they're still alive" scenario. Unless mana has a particular purpose I'm not grasping, or fights are considerably longer than I'd assume they'll be, you're probably going to want mana to be less of a battery and more of a generator.
Secondly, you need 40 mana to have anything other than 1 regen per turn. That's probably not intentional, given that it's extremely difficult to achieve at character creation.
Strength: If main attribute, a 1d8 is rolled. If weakness, a 1d4 is. If neutral, a 1d6 is rolled. A 1d6 is rolled. Every 5 points will increase Health by 10 and Damage rolls by 1.
Agility: If main attribute, a 1d8 is rolled. If weakness, a 1d4 is. If neutral, a 1d6 is rolled. Every 5 points increases Dodge rolls and chance to hit by 1.
Intelligence: If main attribute, a 1d8 is rolled. If weakness, a 1d4 is. If neutral, a 1d6 is rolled. Every 5 points increases Mana by 10 and Regen rate by 1.
I like the more standardized setup for attributes. It's still pretty swingy though- a main-attribute character with a lower score than a weakness-attribute character obviously isn't
likely, but it could happen. Moreso for a main-att below a normal-att, though.
What I don't like is that 5 Str gives you something, and then 6, 7, 8, and 9 Str are no different except that they're getting you closer to 10 Str, which also gives you something. Depending on what you're going for and how the rest of the system works, this could be a necessary sacrifice, or it could be a poorly thought out and swingy system.
I guess the main question is: How do attributes change during play? If they're fairly fluid one way or another, that could potentially make up for the rampant swinginess elsewhere. If the answer is "they don't" or "by leveling up, which happens every now and then," I'm going to have to point out that a lot of characters would be completely useless or deliciously overpowered from the very beginning and in very permanent fashion.