Re: Lost d20, how do you use 3d6 system to replace it lol?
D&D is the main game involving d20s, and (especially in recent versions) its numbers follow fairly specific patterns - which are significantly affected by changing your dice method.
Example:
A fighter is trading blows with an orc. Normally, it takes an 11 or more to connect, so the fighter hits half (50%) the time. This includes all the bonuses from high strength, a normally enchanted weapon, and the like.
The fighter is wielding an exceptionally magical sword, granting a +1 bonus to hit.
With a d20, that's a 55% chance to hit.
With 3d6, it's 62.5% - between a +2 and a +3 to hit on a d20.
Now the fighter also happens to be somewhat stronger than average, for total of +2 to hit.
With a d20, that's a 60% chance to hit.
With 3d6, it's 74% - almost a +5!
The fighter is flanking, gaining +2 to hit from that, and has a magic sword - total of +3 above average.
With a d20, that's a 65% chance to hit.
With 3d6, it's 83% - in the +6 to +7 range.
Flanking, strength, and magic get a +4 to hit.
With a d20, that's a 70% chance to hit.
With 3d6, it's 90%, so +8.
Add a helpful spell, and you can get +5 to hit.
With a d20, that's a 75% chance to hit.
With 3d6, you're a 95%, so +9 to hit - the area in D&D where you only (and always) miss on a 1.
So by putting effort in collecting diverse minor bonuses in D&D, you can get +5 or so to your combat rolls (versus the average). That gives you a nice boost (you hit one and half times more often in the example), but nothing drastic. With 3d6, a +5 bonus is more or less an automatic win...
So switching from d20 to 3d6 means you need to cut down a lot on the bonuses you get in D&D, or you're going to be invincible. Which is great - until you meet someone who has a +5 bonus against you, and you can't win.