First i thought about making the magus ring a hidden entity that only appears after all missions are completed so you can collect it once a playthrough, but i wasn't able to find a flag at your ram map maybe i missed it?
Please tell me if you found it.
Entity hiders don't let you check any flag in RAM. They only let you check the specific flags mentioned in the entity hider docs (boss death flag, misc flag, event flag, currently in middle of a boss fight, game mode). Whether the player has completed all quests isn't one of those so unfortunately you can't use entity hiders for this, though it was a good idea.
Only way to do it is asm, the code to spawn an all-quests-complete pickup needs to be modified so it doesn't check if you have any of the item already. The code that spawns an all-quests-complete pickup starts at 021DD95C. If you change the line that checks how many of the item you have to be "mov r0, 0" it will trick the code into thinking you have 0 of the item regardless of how many you actually have.
And also i added a jumpkick sprite to Richter now, but he seems to be invisible, only his hitboxes are seen, how can i make the sprite visible?
I dunno, I've never had that problem. When I add a new animation to Richter in darkfunction I can immediately use it as his jumpkick animation no problem. Does this gif help?
(Not shown in gif: you need to add 2 hitboxes instead of 1 if you want the jumpkick to damage enemies.)