Fusion Tuner Monsters are simply Fusion Monsters that are also listed as Tuner Monsters, similar to monsters that are Toon, Union or other secondary Monster Types. It was already possible to simply make/treat Fusion Monsters as Tuners (such as with "Lightwave Tuning" or "Dragunity Partisan"). There are very few non-Vortex Synchro Monsters on YCM and this wiki that use this type of monsters for there Synchro Summon, the most prominent examples being "Pitch-Shadow Flash Dragon" and "Solace Dragon". Otherwise, these are still simply both Fusion Monsters and Tuner Monsters with all the rules and conditions that normally apply to both respective types of monsters.

Some Fusion Tuner Monsters share the following condition:

You can also Special Summon this card (from your Extra Deck) by sending the above cards from your hand or field to the GY (in which case you do not use "Polymerization"). If Summoned this way, destroy it during the End Phase of this turn.

Fusion Tuner Monsters are primarily used for the Synchro Summon/Fusion Summon of a Vortex Synchro Monster and the Synchro Summon of a Hyper Synchro Monster.

"Sea Monster of Theseus" is the first, and currenly only, official Fusion Tuner Monster.