Here are a few more examples of size changing abilities...
Size Change (Su): Once per day, a shimnus can change its size in a fashion similar to the effect of an enlarge person spell. The size change from Medium to Huge grants a +16 size bonus to Strength, a –4 size penalty to Dexterity (to a minimum of 1), and a –2 penalty on attack rolls and AC due to its increased size. Its natural reach increases to 15 feet. The shimnus can remain at this size for 10 rounds. This ability is otherwise like the enlarge person spell.
Size Change (Su): At will, spriggans can change their size in a fashion similar to the effect of an enlarge person spell. The size change from Small to Large gains +8 Strength, -4 Dexterity, +6 Constitution and -2 attack bonus and Armor class. A spriggan's short sword has the same attributes as a Large short sword when enlarged. An enlarged spriggan is unable to make a sneak attack or use its spell-like abilities.