You don't even need a necromancer. As you first reach Sorrowing Meadows, the next screen or two would have lots of zombies, who would be tough enough for your current level. Unequip your weapon augment and any rings if they boost attack or Fidget, equip Ugly Pendant, switch to Fidget's first spell type (lots of white projectiles) and fire away. At this point the zombies present would have enough HP for you to reach 9000+ combo, at least on Hardcore (I guess it would be enough on Normal too) - just spam Fidget and replenish energy with normal attacks.

Best way is to equip the Ungly Amulet and spark up the minions summoned by teleporting necromancer in the Sorrowing Meadows.

if you have not destroid the canons yet you can use that as a target, just unequip everything, equip ugly pendent and make sure there are no enemies(i got the achivment legit, gut i were going through the game again and wanted the achivment for 20 sidequest, so i got braging rights when it comes to this one, but if you don't want them go ahead)

lv 18 no sword enhancement pendant or ugly pendant

in 5 mins i got a 2000+ combo in the mansion where you get the brooch by sliding and using lightning

Have an earlier place for this in the Cirramon Caverns. On the 4th cell from the right entrance you can stand on top of a save platform and spam lightning with the ugly pendant.
Got to 3000 before getting bored but still had half the enemies left in the cell at lvl 18 att focused.

I found the best way myself. Basically you do the same you do here, and the only thing you need is Iron Grip and access to Blackmoor Mountains. You go here on the map and you go exactly to this place: http://sp.zhabite.com/sharedfiles/filedetails/?id=858354995
Then just spam Fidget's attack.

I got my 1000 hit combo when I was maxed stats at lvl 60 with all the best equipment. All I did was go to the Sorrowing Meadows, put on the Ugly Pendant and remove all my other equipment (except the Mithararin Robe for defense), find a Necromancer and then spam Fidgets projectiles. Specifically the first ones you unlock. I managed to rack up 2K combo before everything died.

Spamming fire pillars in sorrowing meadows works much easier.

Sorrowing meadows is the best