I remember when I started competitive Pokemon, I would always use the same team of Porygon, Shuckle, Pinsir, Rhydon, Kingdra and Steelix. For the longest time I never really had interest in using other mons.
It wasn't until the release of Pokemon Sun and Moon when I decided to break out and try some of the newer ones.

Since then, I've also looked into some of the older mons as well! My most recent take is with Arbok. I never looked too far into Arbok until I looked up it's stats and movepool. Apparently, Arbok is underrated. Might not be top teir, but it actually got and attack buff in Sun and Moon. It has the ability Intimidate which lowers the opponents attack level, has a respectable attack and speed stat, and has a pretty good movepool! Poison types are a good asset for the current meta with all the Fairy types looming around, it gets Glare which insta paralizes the opponent, Sucker Punch for getting the first hit before the opponent, and even good coverage moves like Aqua Tail!

Another staple asset I have is Clefairy. It has the ability Friend Guard which increases the defense of partner Pokemon in double battles. It has a pretty wide movepool as well. Follow Me directs the opponents attention to Clefairy and away from it's partner, Moonlight which restores HP, and Thunder Wave! It's a very good assist Pokemon!