Fusions, those purple cards with monsters on the end of it. These cards gave birth to idea of syncro and xyz summoning. Why? because it required 2+ monsters to special summon them.
Types of fusions:
These fusions involve 2+ monsters and require a spell card or monster effect to fuse them together. This is considered a special summon. Most fusions now these days have the following text:
This card cannot be special summoned...
This is only true when you do not fusion summon it properly. Once you have and it is in the graveyard for example, we can bring it back to the field using monster reborn assuming the conditions for the fusion have been met.
Notable Cards for Fusion Summoning:
2. Super Polymerization
3. Miracle Fusion (E-Hero's only)
4. Instant Fusion (Different context) - special summons the monster as if it was fusion summoned.
5. Cyber Stien - (refer to Instant fustion)
6. Dark Fusion
7. Summoner of Illusions (refer to Instant Fusion)
Decks that commonly use Basic Fusions: E-Hero, Cyber Dragon decks.
Contact fusion began with Neo spacian monsters in the Yu-gi-oh GX series, in order to summon these monsters you did not require polymerization or cards mentioned above.
All you need is the monsters required for the contact fusion to be on the field face-up OR facedown. Then you send these cards back into the deck, shuffle it, and special summon the monsters.
The more common deck that uses these types of fusions are gladiator beasts.
How to side against it:
Cards that do not allow special summoning:
Vanity's Fiend/Vanity's Ruler
Fossil Dyna Pch....