Okay I know that's kind of self explanatory but I'll give some explanation. I'm playing minecraft and on our current world we've input a rule not to hit mobs. So weapons including bows are off limits for mobs. A bucket of lava is our main tool for killing since technically we aren't attacking it. Simply placing and picking up the lava. Witches don't take damage from lava. So I've done experimenting with dispensers and arrows with redstone and levers and it works but it is not very effective. I'm looking for an effective trap or method of killing witches without actually touching it. No weapons or fishing rods.
Dig a hole, any depth you want. Put at least two pistons on the side, with a block attached to each of them ; build a mecanism to activate them both.
Lure the witch to make her fall in the hole ; crush her.
This can even be done very fast if needed : when in a pinch, first make here fall in a 1x1 wall, cover it so she doesn't throw potions, and you just have to dig again and put your pistons to crush her.
Or just use gravel/sand.
-You can build a tower high enough for fall damage to kill a mob and then use a fishing rod to yank mobs up to you and watch them fall to their death.
-You can make a cheap slime block piston launcher to toss mobs into a pool of lava or a pit.
-You can do the classic piston mob crusher. (I´ve had problems where mobs would walk through blocks and escape before though)
-You can use a tnt duplicator glitch and blow up mobs using an obsidian floor.
Hope this helps add more weapons to your arsenal.