Group: Revolutionary
Posts: 431
Type: Artist
RM Skill: Beginner
Hey there new guy. The first thing that I would do if I were you is to read the help file top to bottom. Seriously, there are some nuggets in that tome that even I don't know about all the way. But for the questions that you asked, here's some answers: Effect rating is the amount that the checked stats are decreased (increased if the target is a party member). For example, if you just want a simple damaging skill, you would put in a number for the effect rating and then check off the HP box to make it do damage.
For a variable chance of causing the poison condition, just change the success rate of the skill. But if you want to do a damaging skill that usually hits 100% but has a 10% chance on top of inducing poison, you'll have to do a bit more work to get that working. I'm pretty sure that it would involve the use of a common event but they can get pretty tricky to utilize in battles due to the events available to choose from are a bit different.
I can tell that you will have a long and confusing road ahead of you. But if you read the help file thoroughly, you will gain understanding like candy from a claw machine (the ones that let you try until you win, of course). Good luck!
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I'd be glad to help anyone with RPG Maker 2003 type questions if they need assistance. Progress: 77%ish (back in action, baby!)