Make Trubbish/Garbodor and Grimer/Muk bitter enemies/rivals

Trubbish is trash, Grimer eats trash, Trubbish stops grimer, etc.. They are bitter rivals

what exactly are you suggesting? how could you make them rivals?

The only way I can think of them being rivals if by doing something similar to Zangoose and Seviper where the two don't breed. However, that won't work since they aren't even in the same egg group anyway.. even then, you might as well make Corsola and Mareanie line 'enemies' due to Mareanie (well Toxapex) hunting Corsola. I mean you could apply the whole not being able to breed thing to them. Other than that, don't see the point of it.

Pokedex, Lose happines together, make Muk/Grimer be able to always defeat Trubissh line.

What? Anyway. Pointless, no canonical reason for it.

I should have worded that better. >.> I meant to say that while Zangoose and Seviper should be able to breed due to sharing the same egg group, their feud makes it impossible to breed on this site. (Assuming the wiki is correct on that)

So... From my personal view, your suggestion doesn't seem to make sense or even possess any coherence. Like what do you mean by "lose happiness together"? Basically like putting the two Pokemon in Daycare and then have them lose happiness that way because they're "rivals"? As far I know, not even the Zangoose/Seviper pair works like that. As HowlingCat already mentioned, the only way this could probably work is if you make them not being able to breed with each other (like Zangoose and Seviper). And even then, they're not in the same egg group so they already can't breed to begin with.

In Poison-type field ONLY, Trubbish loses happiness with Grimer

I wasn't aware that 1% meant impossible.

Then i will go ahead and bring this up in the wiki discussion to one of the editors. *shrugs* Thanks for correcting me.