I haven't seen much action using this card even when Fusions were popular. This card has many uses that many people don't notice. I actually use this card in my Fiend deck.
The most common use is for a fusion-material monster, but its also useful as a defensive monster, though it won't stand up to most monsters used now-a-days.
The Dark - Hex-Sealed Fusion actually has two effects that you can choose to use. If you're Fusion-Summoning a monster, you can use its first ability and use it as a Fusion Substitute. If you don't have Polymerization in your hand, you can use it's second ability to fuse together a proper DARK Fusion Monster. Not only that, but when you use its second ability, you also get its first ability, so you only need to tribute one monster plus this card to special summon a DARK Fusion monster.
Strategies and game play:
If you play a defensive deck, this card is a possibility. If you use a deck that uses a lot of Fusions, like an Elemental Hero deck, this card is practically a staple, as well as its Light and Earth brethren.
And if, for whatever reason, you run out of or can't get out any Polymerizations, you can use its second ability to tribute it and a proper fusion-material to special summon a DARK monster.
Combos with other cards:
This card works wonders in an Elemental Hero or Evil Hero deck. It can be used as a fusion-material for an Elemental Hero deck. It can also be used in two different ways in an Evil Hero deck. Since it's a Rock-type monster, using Dark Fusion or Dark Calling and fusing this card with any fiend will give you Evil Hero Dark Gaia. Since this card is a Fusion-Substitute, fuse this card using or Dark Calling and any Level 6 or Higher Fiend-type monster will give you Evil Hero Malicious Fiend. You can even use Evil Hero Malicious Edge (the card you're subbing this card for) as the Fiend since it's a Level 7 Fiend. And since this card is a fusion-substitute, you can use Dark Fusion or Dark Calling as well as this card and the other proper Fusion-Material to Fusion Summon any of the other Evil Heroes.
Ways to counteract it:
There is no real direct threat with this card's effect, so pretty much the only cards that can stop this card are Fusion-stoppers, such as Anti-Fusion Device or cards that stop special summoning.
* Can be searched via Sangan and Mystic Tomato
* Can be used as a fusion-substitute as well as Polymerization.
* The special summoning of the DARK monster thanks to its second ability isn't considered "proper", so you can't special summon the Fusion Monster from the graveyard using "Monster Reborn", "Re-Fusion", etc...
* 1000-ATK won't defeat most monsters used in today's game, and 1600-DEF isn't a strong defense against most monsters used now-a-days.
* You can't use this monster's second ability to special summon monsters that can only be Fusion Summoned.
The Dark - Hex-Sealed Fusion is available as a common in both Flaming Eternity and Dark Revelations 3.
Artwork and aesthetics:
I like the artwork. Since this monster can be used as a fusion-substitute, there's no specific shape to it. It's just a jumble of different monsters.
In an average deck, 5.5/10
In a Fusion-Heavy deck, 8.5/10