You are mixing APIs here, mysql_* and mysqli_* doesn't mix. You should stick with mysqli_ (as it seems you are anyway), as mysql_* functions are deprecated, and removed entirely in PHP7. 
Your actual issue is a charset problem somewhere. Here's a few pointers which can help you get the right charset for your application. This covers most of the general problems one can face when developing a PHP/MySQL application. 
- ALL attributes throughout your application must be set to UTF-8 
- Save the document as UTF-8 w/o BOM (If you're using Notepad++, it's Format->Convert to UTF-8 w/o BOM)
- The header in both PHP and HTML should be set to UTF-8  - 
- HTML (inside - <head></head>tags):
 - <meta charset="UTF-8">
 
- PHP (at the top of your file, before any output):  - header('Content-Type: text/html; charset=utf-8');
 
 
- Upon connecting to the database, set the charset to UTF-8 for your connection-object, like this (directly after connecting) - mysqli_set_charset($conn, "utf8"); /* Procedural approach */
$conn->set_charset("utf8");        /* Object-oriented approach */
 - This is for - mysqli_*, there are similar ones for- mysql_*and PDO (see bottom of this answer).
 
- Also make sure your database and tables are set to UTF-8, you can do that like this:  - ALTER DATABASE databasename CHARACTER SET utf8 COLLATE utf8_unicode_ci;
ALTER TABLE tablename CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;
 - (Any data already stored won't be converted to the proper charset, so you'll need to do this with a clean database, or update the data after doing this if there are broken characters). 
- If you're using json_encode(), you might need to apply theJSON_UNESCAPED_UNICODEflag, otherwise it will convert special characters to their hexadecimal equivalent.
Remember that EVERYTHING in your entire pipeline of code needs to be set to UFT-8, otherwise you might experience broken characters in your application. 
In addition to this list, there may be functions that has a specific parameter for specifying a charset. The manual will tell you about this (an example is htmlspecialchars()).
There are also special functions for multibyte characters, example: strtolower() won't lower multibyte characters, for that you'll have to use mb_strtolower(), see this live demo.
Note 1: Notice that its someplace noted as utf-8 (with a dash), and someplace as utf8 (without it). It's important that you know when to use which, as they usually aren't interchangeable. For example, HTML and PHP wants utf-8, but MySQL doesn't.
Note 2: In MySQL, "charset" and "collation" is not the same thing, see Difference between Encoding and collation?. Both should be set to utf-8 though; generally collation should be either utf8_general_ci or utf8_unicode_ci, see UTF-8: General? Bin? Unicode?. 
Note 3: If you're using emojis, MySQL needs to be specified with an utf8mb4 charset instead of the standard utf8, both in the database and the connection. HTML and PHP will just have UTF-8. 
Setting UTF-8 with mysql_ and PDO
- PDO: This is done in the DSN of your object. Note the - charsetattribute,
 - $pdo = new PDO("mysql:host=localhost;dbname=database;charset=utf8", "user", "pass");
 
- mysql_: This is done very similar to- mysqli_*, but it doesn't take the connection-object as the first argument.
 - mysql_set_charset('utf8');