I think "
deal 3 damage to 3 random targets, excluding owner." is what you are after for the wording.
If this creature cannot damage itself either, you could use:
"
deal 3 damage to 3 random targets, excluding self and owner."
The mechanic is interesting. The randomness gives it a significant double edge quality.
I think that having itself and its owner excluded from the target list would be a very unique mechanic idea. Basically it would favor having this be the only creature you own...
This could also be interesting if it auto activated whenever a creature was played. That would fit well with a theme of a trigger happy robot. \
What do you think of this: "
: Deal 3 damage to 3 random targets, excluding self and owner. Auto trigger for free when a creature is played." ?