When you use this monster’s second effect, you also get its first effect. So this monster enables you to perform a Special Summon of a Fusion Monster without “Polymerization”, etc., and also acts as a “substitute” for one of the Fusion Material Monsters.
Using the second effect of this monster does not “properly” Fusion Summon the Fusion Monster. So it cannot be revived from the Graveyard, etc. If you use “Polymerization” then you can revive the Fusion Monster from the Graveyard, even if you used this monster as a “substitute” Fusion Material Monster.
To use the second effect of this monster, you must Tribute this monster plus the legal Fusion Material Monster (s) written on the Fusion Monster. For example, to Special Summon “B. Skull Dragon” you must Tribute “The Dark – Hex-Sealed Fusion” as well as either “Red-Eyes B. Dragon” or “Summoned Skull”.
This monster’s second effect cannot be used to Special Summon Fusion Monsters that can only be Summoned by Fusion Summon, such as “Dark Paladin”.