Damn, I feel trolled. I start a topic for Slowbro only for this ancient one to be bummed up. Whatevs. Here's my main points from my Slowbro topic:
So, what's up with Slowbro? For quite a long while, Slowbro has been outclassed by other bulky waters and cursed with a terrible pursuit weakness. He was the perfect Machamp counter last gen, sure, but Hypno is the perfect Breloom counter, and that didn't help his usage out very much. Regeneration and boiling water are just huge boons to him. Seriously, look at this guy:
1) Myriad of support options. Yawn, Thunderwave, Toxic, Boiling Water, Rain Dance, Trick Room, Light Screen, Safeguard, Disable, and even Healing Beam for doubles. Some of these are more viable than others, but the Bro certainly has plenty of options.
2) Regeneration. As mentioned above, this is huge. His pursuit weakness is also mitigated when combined with this. Check out the calcs for 252/ 252 Bold Slowbro:
Adamant 252 Tyranitar's pursuit: 200 - 236 / 50.8% - 59.9%
CB Adamant 252 Scizor's pursuit: 194 - 230 / 49.2% - 58.4%
Adamant 252 Honchkrow's pursuit: 188 - 224 / 47.7% - 56.9%
Do I really need to go on? These are all hitting at about half health, but when regeneration comes into play, the damage is easily solved. I believe these are right, but you're welcome to double check. I used Metalkid's calculator.
3) Instant recovery. One of the most important things for a wall is gifted to Slowbro via Slack Off.
4) Decent special attack with a huge movepool. A base 100 attacking stat doesn't exactly strike terror into the opposing teams, especially if it isn't boosted, but it can get the job done quite well. He can even learn fire blast and flamethrower to roast steels. One can even opt for a gimmicky specs set with regeneration.
5) Slow as crap. This is actually an advantage this gen, as Roopushin can't hit Slowbro with a max power payback. Slowbro can also hit Roo quite hard with STAB psychic.
6) Quite a few options for boosting. Slowking has it beat thanks to nasty plot, but it can learn amnesia, curse, and calm mind. Boosting doesn't exactly mesh well with regeneration, but it remains an option. Amnesia, for instance, can greatly increase Slowbro's survivability.