Monsters are made of 3 parts: Verbum, Imago and Materia.
Verbum and Imago are given at 'birth'. Verbum is a sentence, but only with one independent clause. It affects the monster in unknown ways.
Imago is an image, 500 x 500 or less, suggested by the readers. It affects the appearance of a monster at the start.
Materia are the things equipped by the monster. At the start, the monster may equip one armor and one weapon. It evolves to absorb these, and at the next stage, may equip one piece of armor and one accessory. It will again, absorb these after a while. At the next stage, the monster may equip one piece of accessory before evolving to its final stage.
It is possible for a monster to grow without Materia, and will be a 'pure' monster. Monsters can be combined, but their Verbum and Imago will be unknown. Appearance will be based off both parents. Combination can only be performed on monsters when they're in their max level. The default Max Level is 5, but these can be increased via combination. During combination, a Materia may be used. This affects the monster in unknown ways.
(Unknown ways means that it will not be obvious)
(The names "Verbum, materia and imago" may be changed.)