OSRS - Easy 8:0 Zammy with Bowfa (kill example from fresh instance) 

Door / Altar method (as a learner) is fickle and very prone to error. For learners, 1 mistake likely means tanking 3+ hits from K'ril.
For the 8:0 method, you tank 1-2 hits at the start of the fresh instance and that's it. The benefit of this method is that if you mess up, you can simply follow the numbered tiles and K'ril will fall back in line.
- Greater Demon task preferably
- Ignore the text on my tile markers
- Cannon base MUST be placed to Red-X from tile 2 to 3. This is used strictly for pathing, though you could drop a large Food item and Red-X path to it for the same effect.
- Blood Barrage is a must. Lower level spells don't DPS highly enough.
- Be careful moving from tile 3 to 4, as there is 1 walking tile required to get there. If you attack 1 tile early of tile 4, IMMEDIATELY skip to tile 5, attack, and continue. You will take no damage from K'ril if you react fast enough.