Hello, I am french and this language is a little hard for me so I will explicate speed. I would like do a plugin which give a effect of strong potion but not strong I or strong II but that the player has X% of strong more. Good day !
If you mean they get a X% multiplier to their strength, this is not possible to do with potion effects, since there is no such thing as strength 1.5, just strength I and strength II. However, you can still do this by using EntityDamageByEntityEvent and manually multiplying the amount of damage the player gets, if they're attacked with a player with strength: event.setDamage(event.getDamage() * 1.5));
If you plan on implementing your own system, I would recommend reading this page if you want a similar experience to vanilla.
Ohhh thanks ! You are really amazing, yours answers are perfects for me. I will try and I will come back if I struggle. Good day !