So why should you train your Slayer?
Slayer unlocks monsters that you can't normally kill, with some being the most profitable monsters in the game.
Some of the Slayer bosses bring in millions, the most profitable being the Alchemical Hydra which nets close to 4 mil/hour.
Overall, on your journey to 99 Slayer, you can make a lot of money depending on your playstyle.
Ironmen also get a lot of benefits out of Slayer.
The skill unlocks unique drops like the Abyssal Whip, the Trident, the Occult Necklace and more.
For Ironmen to be raids-ready, they need to train their Slayer for these upgrades.
Another reason to train Slayer is you level your combat stats as you go.
Leveling to 99 Slayer gets you close to 99 in all of the combat stats.
It's efficient combat experience, because your XP per hour is boosted by the effects of the Black Mask or the Slayer Helmet, which give a damage and accuracy boost on Slayer tasks.
10 quests in Old School have a Slayer level requirement.
Some important ones include Desert Treasure 1, Animal Magnetism, The Fremenic Exiles and Monkey Madness 2.
You need level 69 Slayer to get the Quest Cape, and you need level 95 Slayer for the Achievement Diary Cape.