Since you have Filevault - that makes your situation precarious and a bit delicate.

Some good news, Apple has disabled emoji entry in the password pane for 10.11 El Capitan - I can't paste or get emoji in the Users & Groups preference pane.

Apple's official manner to get past this is to click the ? in the password field and reset your password. If you used a recovery key - you can enter it without needing emoji keys. If you used AppleID, you can enter that without needing emoji.

Barring that, If you have a current backup (or can let things complete if you are logged in), the fastest way froward is to wipe the Mac and then restore the backup. You can choose a new password for a new admin account and then import the user files.

If you have ssh enabled, or remote desktop enabled, and the Mac is still logged in to your account, you could log in to the Mac from another Mac over the network. This will not work if you have rebooted the Mac and Recovery HD boot is waiting at the Filevault unlock screen.

If you have a second admin account that is FileVault enabled, you could reboot and use that password to unlock the disk and then reset the password on your main account. Lastly, you could boot to recovery HD or internet recovery and reinstall the OS to a USB drive. Then you can mount the file vault drive and have emoji to unlock the volume and make a new admin account through various tricks / procedures similar to using single user mode to remove the .AppleSetupDone file.