Fusion Summoning is another form of Special Summoning in Yu-Gi-Oh!. As the name states, it involves fusing 2 or more monsters together to make a bigger, stronger monster. One way to Fusion Summon is by using the card Polymerization.
There are various other Spell Cards that allow Fusion Summons, but with different conditions and/or ways to fuse monsters. One example would be Super Polymerization. By discarding a card, it allows you to not only fuse monsters on your side of the field, but with monsters on your opponent's! Another example would be Overload Fusion. Overload Fusion allows you to remove from play Machine-type monsters on your field OR in your graveyard to Fusion Summon a DARK attribute, Machine-type monster.
There are also Fusion Monsters that can be brought out from your Extra Deck without the use of a Polymerization or another Spell Card. One example is Chimeratech Fortress Dragon. It can be special summoned from your extra deck by removing from play face-up Machine-type monsters on both player's fields. Another example is the Gladiator Beast Fusion Monsters. There are 3 Gladiator Beast Fusion Monsters: Gladiator Beast Heraklinos, Gladiator Beast Gyzarus, and Gladiator Beast Gaiodaz. All 3 can be special summoned from your extra deck by returning to your deck the monsters that are required to Fusion Summon it.
Fusion Summoning has become less popular nowadays due to the release of Synchro Monsters, however some Fusion Monsters are still worth putting into your Extra Deck. One of the most popular Fusion Monsters nowadays is Chimeratech Fortress Dragon. Many players put this into their Extra Deck when they play against a deck using Machine-type monsters. Not only does it get rid of their face-up Machine-type monsters, but it gives you a gigantic monster to control. Another Fusion Monster, or should I say two Fusion Monsters, that are popular nowadays is Gladiator Beast Gyzarus and Gladiator Beast Heraklinos. Gladiator Beast Gyzarus can destroy cards when it is special summoned from the extra deck, and Gladiator Beast Heraklinos can negate your opponent's Spell and Trap Cards. Both cards are widely used in Gladiator Beast Decks. Finally, another Fusion Monster worth mentioning is Five-Headed Dragon. It is a massive Fusion Monster that, at first glance, seems very hard to summon. However, a new deck called Disaster Dragon, and other variants of it, have been able to summon this monster with relative ease. By using the Spell Card Future Fusion, it sends 5 Dragon-type monsters from your deck to the graveyard. Then, if Future Fusion survives for 2 turns, it brings out the 5000 Attack and Defense Fusion Monster, that is almost impossible to destroy by battle. In the deck Disaster Dragon, a good combo can be executed by using Future Fusion, Five-Headed Dragon, 2 Red-Eyes Darkness Metal Dragons, and 2 Red-Eyes Wyverns. When you activate Future Fusion while you have 2 Red-Eyes Darkness Metal Dragons and 2 Red-Eyes Wyverns in your deck and you activate Future Fusion, send those 4 and 1 other Dragon-type monster to the graveyard. Then, later in your turn, you can use your 2 Red-Eyes Wyverns' effects in your Graveyard to Special Summon the 2 Red-Eyes Darkness Metal Dragons.
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