In short, no. But they are definitely worth battling!
Shadow Behemoths are shadow versions of original SS- and S-ranked Behemoths.
|Original Behemoth||Shadow Behemoth|
|Deus Felnarog||Shadow Felnarog|
|Leider Reaper||Shadow Reaper|
What this means is that you do not get Tablets (for forging new equipment) when you defeat Shadow Behemoths in battle. However, you’ll get the materials needed to enhance (level up/evolve) your equipment.
Defeat the original Behemoth first, so that you can use the Tablet to forge equipment. But forging is only the beginning.
A S-ranked weapon typically has 40 levels, and that’s before evolution. You’ll need lots of materials to enhance it, and that’s where Shadow Behemoths come in. When you defeat Shadow Behemoths, you’ll get the materials needed to enhance your equipment.
Tip: Higher-level Behemoths drop more higher-grade materials.
You can challenge up to 5 Shadow Behemoths a day.
TLDR: To forge new equipment, defeat original Behemoths.
To enhance equipment, defeat Shadow Behemoths.