you might want to make traps and thair are ways to do this.
you will need a lot of dynamite and then go make a explosives you will need a wire and 3 dynamite
it is the one you can occasionaly find in caves
it is placeable and can be activated by a lever or a button or a presure plate
for best results use a presure plate and place the explosive under the desired target and kabloom its gone.

you may want to do something to your friend instead of his world
for this to work rig a cave with dart traps just the ones you can find in a regular cave will do
then make some presure plates and then put wire connecting them then put the preasure plate down
some ware random and then leave the cave like you were just exploreing if you want to do more that darts
then make a giant cave explosion just put the dynamite bomb in a lot of random not obvious places
then rig it to a lever in the cave he will maby think it leads to a secret cave instead of this he will die
and lose a lot of stuff if not on softcore if on soft core he will lose a lot of coins never admit that you messed with the cave

these are traps that are difficult to get
they are found in the lizhard temple they are danger,us.
they can kill a player verey fast thair is a spear trap that impails the player.
then they,res flame traps that burn a player setting the debuff onfire.
then thair is the spikey ball trap that drops a spiky ball that damages the player super fast.
set more traps in the temple in the world you want to do /friends world
then make sure you have covered up your work becuse your friend will get mad but wont know who