I'm trying to think back on how much you've missed....Are you familiar with "Contact Fusion"? Basically, some of the Elemental Heroes came out that can only be Fused like the XYZ Dragons of old, where you send them from you side of the Field. Well a group of Monsters called Gladiator Beasts can do that too (Gladiator Beast is in their Name, not type or subtype). All these can be "Contact Fusioned" while Face-Down, just show your opponent the cards you are using.
Synchro-summoning is different. The Synchro Material Monsters (SMM) must be Face-Up to Synchro Summon. All of these Summons are considered Inherant Summons for the purpose of Solemn Judgement, (Black) Horn of Heaven, etc. And since Fusing and Synchroing are not a cost, but the resolution of an effect, you can do them with Macro Cosmos on the field.
Also, Gemini Monsters were mentioned. In case you weren't around for those, they are sub-type Gemini and are effect Monsters that are treated as Normal Monsters in the Graveyard or on the Field; but, you can use your once per turn Summon to Summon them again and they gain their effect(s).
So, 2 new sub-types, 1 new type, an old summoning mechanic, made new again, and a full on new card genre. Stay "tuned", because there is yet another genre potentially coming that uses subtraction, rather than addition to make your "sychros".