This cards effect does not require a sacrifice to resurrect a unit from your drop zone like the other resurrect cards like Samurai Spirit, Deadly Nightmare or Deadly Spirit, but it DOES require you to use an extra counter blast to use. When you don't have any cards you want to sacrifice, or you need to keep cards in your hand for defending, you can always use cards like this to call other cards from your drop zone without having to sacrifice anything.
You can use self-resurrecting cards to sacrifice this unit after using its ability. Since Negromarl's ability is best served as a free resurrection, it isn't of much use after using it for attack or defense. That way, it is best used as tribute folder to trade for much higher attack from Dragon Undead, Skull Dragon or use it to maintain Defensive Intercepting from Captain Nightmist or Deadly Spirit during your opponent's turn.
Offensively, you can use this card in combination with Death Seeker, Thanatos. After you hit the vanguard with Thanatos' attack, you can use his ability to Sacrifice himself and Resurrect Negromarl, and then use Negromarl's skill to counter blast 2 to call Thanatos back onto the field, or some other card from your graveyard like Skull Dragon. That gives you an extra two attacks during your battle phase for a counter blast of 3. Given, that isn't cheap compared to some other decks (like Pale Moon or Spike Brothers) it still gives GranBlue that extra Push they need.
If you use a deck that is focused on this cards effect, you HAVE to use Three Star Chef, Pietro to keep refreshing your damage. That is because you will constantly counter blasting to resurrect cards from your graveyard, unless your using soul blast 2 self-resurrecting cards. That makes it hard to keep using counter blasting over and over again, when most combo's using Negromarl's effect uses two or more counter blasts every time you do it.
If you are short of cards on the field, you can ride Ice Prison Necromancer, Cocytus and counter blast 2 to call this unit, and uses another 2 more counter blasts for this unit's skill to call another grade 2 or grade 3 from your Drop Zone.
You can use this card's skill to call a Dancing Cutlass or Rough Seas Banshee and uses the respective cards' skill to draw an extra card. Furthermore, with boost from Dancing Cutlass, this card could swing for 13k, enough to reach the minimum power required to attack crossriders. Similarly, you could call a Ripple Banshee to give this card an extra 2K power for the turn.