Risen

This can be achieved by bringing any of the three attributes to a natural 200, meaning you cannot use any rings or amulets to boost. Dexterity is probably the easiest as you'll find more Dex boosting items than Str. Trainers will only train you to 100. To raise the remaining points you are going to rely mainly on brewing potions that give +5 in strength or dexterity. For this you need Alchemy level 3, Hero's Crown plants (of which there are 20 total in the game), and last the plant for Strength or Dexterity, Ogreroots or Pixie Hats respectively. The recipes for brewing these potions can be found hidden, or bought from the alchemists after Chapter 2.

To effectively maximize a skill, train it up to 100, then consume any attribute boosters you have for that skill up to the nearest 5, and finally brew as many +5 potions you need to reach 200. Commonly know 'boosters' are eating 50 apples for +5 strength, Harlok's stew in the monastery for +2 strength (Mage only), and the Hunter's Fry-up recipe found in the chest behind Patty when in Harbour Town for +2 dexterity. Also realize since there are only 20 Hero's Crown total in the game, once they are spent, you might as well eat the remaining attribute plants.