How do I make sure that after I hit the mob with a custom sword, any effect is superimposed on me?

What do you mean with superimposed?

With which kinda sword? If you have created a custom sword and want it to effect you, when you are in the element of the sword you want to do it on, you want to go to triggers and then, when living entity hit with tool. In there you want to create a procedure and in the procedure, you will just drag in a "add potion with level" block and then you can choose for how long and what effect, hopefully this is what you are looking for! Hit me up if theres something wrong! If you dont understand, feel free to add me on discord: FluffigBoll#3084