diff --git a/src/guide/mutators.md b/src/guide/mutators.md
index 774e0acc..2318ba97 100644
--- a/src/guide/mutators.md
+++ b/src/guide/mutators.md
@@ -292,7 +292,54 @@ infection.json:
 | CastString | `(string) $value;` | `$value` |
 
 ### Regex
+
 | Name | Original | Mutated |
 | :------: | :------: |:-------:|
 | PregQuote | `$a = preg_quote('text');` | `$a = 'text';` |
 | PregMatchMatches | `preg_match('/pattern/', $value, $matches);` | `(int) $matches = array();` |
+
+### Extensions
+
+|   Name   | Original | Mutated |
+| :------: | :------: |:-------:|
+| MBString | `mb_chr($code);` | `chr($code);` |
+|          | `mb_ord($character);` | `ord($character);` |
+|          | `mb_parse_str('text', $results);` | `parse_str('text', $results);` |
+|          | `mb_send_mail($to, $subject, $message, $headers, $parameters);` | `mail($to, $subject, $message, $headers, $parameters);` |
+|          | `mb_strcut('text', 0, 123, 'utf-8');` | `substr('text', 0, 123);` |
+|          | `mb_stripos('text', 't', 0, 'utf-8');` | `stripos('text', 't', 0);` |
+|          | `mb_stristr('text', 't', true, 'utf-8');` | `stristr('text', 't', true);` |
+|          | `mb_strlen('text', 'utf-8');` | `strlen('text');` |
+|          | `mb_strpos('text', 't', 0, 'utf-8');` | `strpos('text', 't', 0);` |
+|          | `mb_strrchr('text', 't', true, 'utf-8');` | `strrchr('text', 't', true);` |
+|          | `mb_strripos('text', 't', 0, 'utf-8');` | `strripos('text', 't', 0);` |
+|          | `mb_strrpos('text', 't', 0, 'utf-8');` | `strrpos('text', 't', 0);` |
+|          | `mb_strstr('text', 't', true, 'utf-8');` | `strstr('text', 't', true);` |
+|          | `mb_strtolower('text', 'utf-8');` | `strtolower('text');` |
+|          | `mb_strtoupper('text', 'utf-8');` | `strtoupper('text');` |
+|          | `mb_substr_count('text', 't', 'utf-8');` | `substr_count('text', 't');` |
+|          | `mb_substr('text', 0, 123, 'utf-8');` | `substr('text', 0, 123);` |
+|          | `mb_convert_case('text', $mode);` | `strtoupper('text');`, `strtolower('text');` or `ucwords('text');` depending on mode |
+
+#### `MBString`
+
+ * `"mb_parse_str": true`: You are able to disable any of the supported mb string functions. All supported functions are enabled by default.
+
+> Some of the functions are not supported due to complexity to convert them to standard string manipulation functions.
+> Implementing them either does not make sense or creates too many false positive mutations.
+> Not supported functions are `mb_ereg*`, `mb_split`, `mb_strrichr`, `mb_get_info` and similar.
+
+infection.json:
+
+```json
+{
+    "mutators": {
+        "MBString": {
+            "settings": {
+                "mb_send_mail": false,
+                "mb_substr_count": false
+            }
+        }
+     }
+}
+```
diff --git a/src/guide/profiles.md b/src/guide/profiles.md
index 8ab0fa59..2f631224 100644
--- a/src/guide/profiles.md
+++ b/src/guide/profiles.md
@@ -247,6 +247,12 @@ Contains the following mutators:
 * [Foreach_](/guide/mutators.html#Loop)
 * [For_](/guide/mutators.html#Loop)
 
+### `@extensions`
+
+Contains the following mutators:
+
+ * [MBString](/guide/mutators.html#Extensions)
+
 ### `@default`
 
 This is the default profile, which currently contains **most** mutators, and is used if no mutator or profile is chosen.