Defence Matters - OSRS Combat Achievements

5-tick range/mage weapon or faster.
Any crossbow on rapid will also work.
I used Bow of Faerdhinen on accurate.
Example gear/inventory setup at start, downgrade/upgrade as necessary.

Setup kill is not necessary, you will only take damage from Graardor which will not fail this challenge. This should complete the "Keep Away" task simultaneously if Graardor doesn't range you at the start.

This is much more consistent than the cheesy tank setups that only flick the minions and you get 2 hit by the boss.

You will have to perform an action every tick for a 5-tick cycle and repeat.
Metronome and visual metronome could be useful for this.
Start the kill with high prayer points, HP, potted and stamina as it will be difficult to stay in cycle and click items in your inventory.
Quick prayers should be protect range and offensive prayers.
10/10 would recommend very fun/rewarding to learn.

Method:
wait 1 tick after Graardor spawns
attack
react to ranger attack, pray mage
pray melee
click manta
wait 1 tick
pray range
pray mage
attack, click manta
pray melee
pray range
pray mage
attack, click the farther manta

repeat attacking, pray flicks and clicking the manta for red x

END the kill on the Northwest blue tile, then run south 2 tiles otherwise the meleer will not be off ticked.
If Graardor dies and you're on the south east blue tile, wait a tick and run northwest whilst continuing your pray flicks till the meleer hits you.
It is necessary to kill the minions whist pray flicking them otherwise they will mess up the pray flicks the following kill.

Tips:
If you are attacking early - react to the boss spawn, click your quick prays then attack the boss. This is what helped me.
If you pick up your red X item - you did not attack on the right tick, true tile indicator might help
Pick an item with a large click box on the ground i.e. manta ray

Tiles - Only need the 2 blue tiles (this is where you drop your items for red X) and the tile labeled "start dont shoot" ignore the "start dont shoot" advice that does not apply here.

My tile markers:
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