a pagina 29 del DM nel paragrafo mescolare il tutto dice:"due creature le cui taglie non differiscano di almeno due categorie l'una dall'altra non possono occupare lo stesso spazio in combattimento".

supponiamo di avere un verme mostruoso minuscolo contro un halfling, visto che il verme non può entrare nell'area dell'halfling riceve un attacco di opp. ogni volta che tenta di attaccare???

Si, deve spostarsi ogni volta.

Tiny, Diminutive, and Fine Creatures: Very small creatures take up less than 1 square of space. This means that more than one such creature can fit into a single square. A Tiny creature typically occupies a space only 2-1/2 feet across, so four can fit into a single square. Twenty-five Diminutive creatures or 100 Fine creatures can fit into a single square. Creatures that take up less than 1 square of space typically have a natural reach of 0 feet, meaning they can’t reach into adjacent squares. They must enter an opponent’s square to attack in melee. This provokes an attack of opportunity from the opponent. You can attack into your own square if you need to, so you can attack such creatures normally. Since they have no natural reach, they do not threaten the squares around them. You can move past them without provoking attacks of opportunity. They also can’t flank an enemy.