rules updates

add dread wurm and werebeasts
fix backlink for magic items
update rules for + abilities

src/pages/rules/basics.md

@@ -25,7 +25,7 @@ Sometimes, dice are rolled. These dice are described by how many sides they have
 
 Simple tasks are assumed to succeed. If the task is dangerous or complicated, roll the dice for a _check_.
 
-For most checks, roll a 20-sided die (d20) at-or-over the difference of (21 - the character's most relevant _ability_ score).
+For most checks, roll a 20-sided die (d20) **over** the difference of (20 - the character's most relevant _ability_ score).
 
 -   For harder tasks, subtract 1-4 from the roll before the die is thrown.