Celvin found himself within a forest, without memories. Thankfully an interactive menu appeared in front of him explaining what had happened. According to Menu-san, He was a japanese who died because of God's mistake then reincarnated in isekai with cheat. In order for more cheats, like S-class Summoning, he exchanged his memories for them. One of those cheats is to have the Goddess of Reincarnation Melfina to be his subordinate, and yes Menu-san turns out to be the Goddess. But his initial MP wasn't sufficient to materialize her, so in order to raise his status from that moment on Celvin started his journey as battle junkie.

1. Is the MC OP?
The Black Summoner Who Was Stronger than Even the Hero

2. Is this a harem?
Undoubtedly

3. Is there snusnu in this novel?
She asked to be eaten, so she was eaten

1)Goddess ->later in the story she gets an artificial body so she can join in the adventure
2)Slime ->Can absorb energy from bodies/items and turn it into a laser attack.Gets used as inventory too so that they can change weapons/armor during fights (he separates into small pieces and hides in gauntlets etc)
3) Ghost Knight ->a real bro, a little of pedo(? don't really remember)
4)Elf slave ->don't know how the plot went since i dropped right before her arc started but she has a dragon's fire powers she uses together with archery (basically flame arrows with lock on function)
5)Little sick girl he summoned from another world with hero ritual
6)Shadow wolf, fights together with the hero girl. Uses sword (basically think of that boss from demon soul game or whatever its name is)
And this is as far as i know his party.

the kingdom they were fighting had an army of like 3000 dragons and 5-6 really strong ones they had to enslave to use he mc pretty much ambushes and owns them all with his harem and then frees all the top dragons and makes them his summons

the strongest black dragon is a farmer dragon who likes vegetables and hated how they only fed him raw meat when he was enslaved he can transform into human form and talks like a yakuza calling the mc aniki also he falls in love with pretty-chan the muscle okama(?)

The one with Efil (half elf, her name is just a permutation of elf anyway) is a bit hard to spot as till he snusnu other harem member it is only too elusively references (till the point that it is impossible to guess whether yes or not), well in afforementioned time it is revealed that yes. The only other is with Sela(daughter of maou, 1st-2nd best heroin) (this one is hard to miss though).

It also seems like Mel (goddess) is nearing this quite fast. His self proclaimed imouto Lion (poisoned by reading incest novels and manga) is also doing her best to reach the furthest possible except for the last step. Well till bathing together for the moment, and might never cross the line as, well she behaves as his little sister for the time being (in LN/manga sense, whether she read only 15+ or read even 18+ is yet to be mentioned :) )