To all the experience veteran and pros, calm down. This is not for you. I know you have a better method, a more reliable method, and a more "legit" consistent method. But those are costly and time consuming. This is for the newbie who wants to explore all the map, the ones who just want the badge for w/e reason and do not care how they get there.
More explanation to who this is for:
This guide is for newbies who want to just to be able to beat guardians and travel to anywhere in the map, or want to beat arenas, or just any npc really.
This is only beneficial to newbies who do not own any strong monsters to beat the arena and guardian in a fair fight.
This is basically the same as catching ancients, you need low level monsters, and you need a move that makes the opponent have the same hp as you, like level off, tuning fork, short circuit, equality, ect...
the only difference is that now you need the ability, "Radiation"
Ability that increases your evasion and decreases enemy accuracy helps, as well as evasion armor.
Now there is also the issue of those monsters that have expert regen, or has an orb that heals them. I suggest you try to get a status effect move that inflicts burn, poison or bleed on all your monsters.
If u can get a reliable method of doing this do so. mine was:
now you just have to cast the dice or flip the coin, and just spam level off until all the enemy is dead. If you die, try again, sooner or later, you will get lucky and eventually win.