Is it worth it to teach Toxic to a Pokemon? Why or why not?
Yes if you know how to use it. First you use toxic, then protect and attack them next and then just protect and attack over and over until it dies. Since toxic gains power each turn.
Pokemonblack10's strategy is pretty good. Even without using Protect it's a great move.
You could also use Toxic Spikes so that all pokemon switching in get poisoned. One set of spikes = they get poisoned, two = badly poisoned.