Chickens, Ducks, Rats (small ones), and Spiders (The small ones)
have -42 magic defense
Men/Women have -21 magic defense
Goblins have -15 magic defense
Black Kinights have -11 magic defense
Lesser, greater, and black demons have -10 magic defense.
I’d just use fire strike.
Good-luck.
Edit: You can also splash ‘curse’ on the monk of zamorak in varrock castle. Wear full melee when you do this. You want as much negative magic accuracy as possible. This does not give HP xp.
Damage is calculated by the spell. Accuracy is calculated by magic offense and magic level. So yes, robe top, wizard hat (black or blue), a staff, and an amulet of magic would help.
Edit: If you are trying to splash you’ll want to get as close as you can to -64 magic so you’d want to wear melee armour and vambraces if you can.