As Tang Shaoyang approached the defeated spirit, he checked the window status. The shield consumed 300 Slayer Energy while the skill [Slayer Blade] consumed 100 Slayer Energy per blade.

Aside from the lower cost, using Slayer Energy was more efficient. Also, the Slayer Energy used for skill was more refined than controlling it without using the skill. He could tell the difference within a glance.

"It seems I have to control the Slayer Energy better for efficient use and stronger form of the energy…" Tang Shaoyang arrived next to the specter. The Slayer Blade pinned Furi the Specter down. It could not move after a few simple exchanges.

Tang Shaoyang then extended his hand toward the spirit.

[Do you want to sacrifice Grade A+ Spirit, Furi the Specter? Yes/No?]

After some consideration, Tang Shaoyang decided to sacrifice the spirit.

[You have sacrificed Grade A+ Spirit, Furi the Specter!]

[You gained 8 Levels and a random skill of Furi the Specter!]

[You obtained a skill, Gravity Pull!]

[You gained 5 Spirit Power!]

"It seems I obtained a useful skill this time," He muttered after the consecutive notification. Even so, he furrowed his brows, displeased despite a free skill and also a free level.

"8 levels? Why? This is Grade A+ Spirit," he was displeased with the levels he got. He gained 22 levels by sacrificing Grade B+ Spirit, yet it was only 8 levels for Grade A+ Spirit.

—That must be because of the advancement. You should expect this to happen. The Spirit Sacrifice would be less effective as you keep getting stronger.

Zanoes voiced his thoughts. This was something he expected to happen. Since this was a game, there must be a balance in the game, and if the [Spirit Sacrifice] gave the same levels despite the advancement. [Spirit Contractor] would break the balance of the game.

"But 8 levels were still too low. I thought it would be around 20 levels or maybe 15 levels," Tang Shaoyang shook his head, "Does this mean it's better if I summon a Grade B Spirit than a higher grade spirit? The amount of the sacrifices is too big between the two grades while the gain is not that much!"

He sacrificed twenty thousand zombies for Grade B+ Spirit and four thousand zombies for Grade A+ Spirit. 20 times sacrifices were needed for Grade A+ Spirit but the gain was not even double that of Grade B Spirit.

—if the level is what you want, you indeed better summon Grade B Spirit, but if you aim to contract a spirit or even aim to get the skill, a higher spirit is the best.

That was what the reliable spirit told him.

—However, if I guess correctly the Grade B Spirit will only give you one or even two levels.

"What about this Spiritual Power?" There was an additional gain, Spiritual Power. That was the newly obtained attribute after he advanced to [Spirit King].

He got 5 Spirit Power and now he had 50 Spirit Energy. He noticed that when he checked the window status.

"This must be related to the new skill and the skill I can't use before," Tang Shaoyang muttered in a low voice.

[Spirit Form], he tried to use that skill once, but he could not because he did not have Spirit Energy. It said that he needed Spirit Energy to use the skill as mana did not work with the skill.

Another new skill, [Spirit Gate]. He had not tried it yet, but Spirit Energy was needed most likely to use the skill. He then tried to cast the skill, [Spirit Gate].

[You don't have enough Spirit Energy to form Spirit Gate!]

"As I thought… What about the other one," He muttered in a low voice as he cast [Spirit Form].

To his surprise, his body blurred and became transparent. He could see the frame of his figure but he had become transparent like the spirit. Five seconds later, his body returned to normal.

"50 Spirit Energy only lasts for five seconds…" He finally realized the three skills were related.

[Spirit Energy] was needed in order to use [Spirit Form] and [Spirit Gate]. [Spirit Gate] most likely to form a gate to a spirit world. In order to enter the spirit world, he had to be in [Spirit Form].

"But that's weird that I got [Spirit Form] first instead of [Spirit Energy]," Tang Shaoyang muttered as the order he obtained the skill was somehow reversed.

"Nah, whatever, it does not matter. Now I have the skill…" then he realized something, "If the [Spirit Gate] can lead me to Spirit World, does that mean I can sacrifice and contract all the spirits I meet there?"

—I think it will not be that simple. There must be some kind of restriction or something. Moreover, does the Spirit World exist? Maybe the Spirit Gate can lead you to another world, but not a Spirit World. Before you summoned me, it was just eternal darkness.

Zaneos spoke his piece. Not that he tried to discourage his Master, but that was the truth. He did not come from Spirit World.

"We will know once we can use the skill," Tang Shaoyang was not discouraged as he believed that either Spirit World or another world, both would benefit him in some way.

"Let's continue with the next summoning, Grade B Spirit, fifteen thousand zombies," Tang Shaoyang summoned Grade B Spirit to test out the gain from sacrificing such spirit.

…

[Do you want to sacrifice Grade B Spirit, Leam the Undead Knight? Yes/No?]

[You have sacrificed Grade B Spirit, Leam the Undead Knight!]

[You gained 1 level and a random skill of Leam the Undead Knight!]

[You obtained a skill, [Charge]!]

[You gained 1 Spirit Power!]

[Friction skill detected! Initiating skill fusion, [Deadly Charge] and [Charge]!]

[Skill fusion failed! [Deadly Charge] is a superior grade skill than [Charge]!]

[Skill [Charge] has been removed!]

Zaneos guessed right, he now only obtained 1 level and also 1 Spirit Power. No skill since Skill Fusion triggered and failed at the same time. The gain from sacrificing Grade B Spirit was minuscule.

"You guessed right, Teacher. The gain is minuscule, though if I truly aim for the level, I should have summoned Grade B Spirit," Tang Shaoyang said. He could no longer abuse [Spirit Sacrifice] as before.