Yep Giant Spider is a great troop to go along with Infernus. Been having fun with:
Gorgotha or Dark Troll
EDIT: Since GS has Magic Link I'll use either Orc Banner (for fast Dark Troll) or Wolf Banner (for fast Spider).
Infernus needs to be fully traited to use Elem effectively, and it's super nice (though not required) to have Elem's attack reduction trait also. Use Gorgotha for safer team and Dark Troll to get purple gems galore, especially after a GS or Elem cast. Since Darkness appears to trigger on each individual 4+ match having a board fill with purple will have all of the enemy down to zero attack in no time.
What the heck, this sounds more like an Elemaugrim post then praising Infernus! His Conflagration trait is just along for the ride providing a spawn boost, but his spell can pick off weakened enemies.