Adding potion effect to a weapons

You can't :( It will give the potion effect to you, not to the target entity

Maybe you could create a procedure which when you attack the opponent it drops a splash potion and then clears the effect from you

You're right... I should try to make a Poisonous Sword that poisons the enemy

When I posted that reply I forgot that commands give command output unless you have the gamerule commandblockoutput set to false.

It's weird to see a command output everytime you use your weapon but it's also weird to change the gamerule while the player didn't want to change it...

Sorry for bad English

hmmmm yeah

after you do the poison you could set command output to false again

this is my code so far

Whoops the first and last block is meant to be switched around

Yes, I have thought of that, but if the gamerule was already false before using the poisonous sword? The procedure will set it to true and the player will be forced to set it to false manually everytime he uses the poisonous sword.

Anyways it should work for players that don't use commands in survival minecraft (most of players, I think) (anyways, who would use that gamerule in survival? XD)

Sorry for bad English

Sorry, I didn't see your comment that said exactly what did I say in my last comment XD

You can use "effect @e[range=2] poison 5" for making only near mobs being affected by the poison

I think I will add the poison effect sword in my mod, who cares of the gamerule XD

Sorry for 3 comments in a row...

Sorry, wrong command

The command I am using is

effect @e[type=!player,r=3,rm=0] minecraft:poison 5

Sorry for another comment :(

The gamerule commandblockoutput doesn't seem to work with chat commands

Well, even though you could possibly get it to work this way,  you can just override Item#hitEntity() and do it properly.

So how exactly would this work?