Richter is an echo fighter of 
Simon. Richter's moves, framedata, and everything else besides the aesthetics of certain animations can be considered identical to Simon's. The only crucial difference between the two characters is Holy Water (Down-B).
Richter's Holy Water has aura properties, while Simon's Holy Water has fire properties. This affects how each move interacts with certain characters' moves and items. Firstly, do not be fooled by the aura properties of Richter's Holy Water, for it does not scale with damage like 
Lucario's Aura mechanic would. Second, this difference is only necessary to a few characters. Richter notably does better against 
Olimar than Simon does because his aura Holy Water will damage Red Pikmin while Simon's will not. However, Simon's fire Holy Water will cause certain explosives, notably 
Link's Remote Bomb and 
Steve's TNT, to explode while Richter's will not. These differences are not important except in very specific scenarios--particularly when Link is holding a Remote Bomb, drops it due to taking damage from Holy Water, and the fire causes the bomb to explode--so just pick whichever Belmont you prefer.
You can read up on the differences at SSBWiki.
You can read up on the documentation that effectively covers both of these characters on Simon's character page.
Essentials
• Controls • FAQ •
The Basics
• Movement •
Offense •
Defense •
Detailed & Advanced Information
• Damage/Knockback • Frame Data Explanations • States of Play • Universal Strategy • Esoterica •
Archived Information
• Patch Notes • Tier Lists • Alternate Resources • Discords •
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