From Melvor Idle

A template for quickly building monster links with icons. For example, {{MonsterIcon|Golbin}} becomes Golbin (monster).svg Golbin.

Adding a second argument allows you to override the text. For example, {{MonsterIcon|Golbin|No, it isn't a typo}} gives Golbin (monster).svg No, it isn't a typo.

For a complete list of options, please refer to Template:Icon.