My suggestion would be introduce greater versions of some of the monsters as Bosses to have variety in choice whether to slay normal ones or bigger ones and a lot more challenging. For instance, Hellhounds. Boss version - Greater Hellhound(Instanced place, so other players won't bother you against it) Naturally, Boss coming in game means having something unique to work on, so even with Helldog as pet it won't be any sort of challenge to do, therefore I came up with more advanced skilling improvment called Inferno equipment. While it is implemented in RS3, in Emps it would be named as Fiery. Greater Hellhound will have a chance of 1 in 250 dropping Fiery Stone. You wondering how actually it could be working in a manner to use in Emps? Fiery Stone Combined with ONLY Dragon Hatchet would give Fiery Hatchet being able to use it requires 92 Woodcutting. After 10000 uses, Fiery Stone will seperate from hatchet and instantly turns to dust. Having this stone would increase the rate of gathering crushed nest, though bonus doesn't stack with rabbit foot necklace (not sure if it gives any bonuses). Besides this, where it should be located? Adding obstacle near Hellhounds in Barbarian Village could be idea, though I'm open to see what you think about it as Boss version for tasks as well. Slayer exp per kill would be around 2300~ exp and since it's instanced place you would need to re-enter it. Slayer level required 89. Combat Level 529, Hitpoints 270. Attacks with all three styles around 30 per style. Weaker to ranged attacks or ice/water spells.
Drop table can be edited likewise, it doesn't supposed to be like something I listed. As for Fiery equipment, since Emps is having Obsidian overlay we could collaborate it with Fiery making it look somewhat obsidian and dragon enchantment. Design is up to higher Ups or players who can make one, I just invoked idea, sorry, don't have so much design skills up my sleeves to show it...
EDITED: Also added Fiery blade's claw, attachable to dragon scimitar, making as weapon in single-handed weapon slot, with gives almost as good stats as whips, but with special attack, which boosts it's usage, it becomes stronger than Saradomin Sword for 2 minutes. 70 Attack required to equip it. After 10000 uses, it turns to dust, and in inventory you will either receive claw or scimitar ratio being 1:1.
Fiery Crossbow requires 85 ranged, fires any type of bolts, including kebbit bolts, has a special attack working like Saradomin Godsword, only with prayer healing and not hitpoints.
Drop Table:
3 - Super Restores (4)
3 - Saradomin Brews (4)
3 - Zamorak Brews (4)
5 - Super Combat (4)
4 - Super Ranging (4)
4 - Super Magic (4)
10250 - 46150 - Coins
10 - 55 Bowstring
960 - 1200 Arrowshafts
100 - 150 Dragon Bolt Tips
7 - 44 Runite Bolts
1 - 5 Grimy Snapdragon(noted)
1 - 5 Grimy Toadflax(noted)
1 - 6 Grimy Dwarf Weed(noted)
1 - 4 Grimy Kwuarm(noted)
10 - 53 Mithril Ore(noted)
2 - 15 Adamant Bars(noted)
22 - 78 Gold Ore(noted)
1 - 9 Rune Bar(noted)
1 - 6 Sharks
1 - 4 Manta Ray
10 - 33 Magic Logs(noted)
1 - 3 Uncut Dragonstone
1 - Fiery Stone(1 in 250 drop)
25 - 30 - Mystic Fire Staff(1 in 100 drop) <- Good Alchs for those who don't know why it's here.
7 - 20 - Burnt Bones(noted)
1 - Hell-Doggy (1 in 1000 drop)
1 - Fiery Blade's Claw(1 in 250 drop)
1 - Fiery Crossbow (1 in 250 drop)