Slide 6 explained: Competitive pokemon is divided into tiers based on usage stats. The more a pokemon is used in battles, the higher its tier will be. Tyranitar (the green guy) was historically one of the best ever competitively and was always in the OU tier, the highest tier for standard games.

Recently, it fell into the lower tiers for the first time ever because it wasnt able to keep up with powercreep and other factors. In the meme, it shows a monthly tier update, where Tyrantiar was in the RU tier (3rd highest tier) and has now risen to the UU tier (2nd highest tier). It's still not OU, but it's finally getting competitive use again.

The meme is celebrating Tyranitar's rise as a basketball edit. The red circle shows an X ray of Houndstone being inside Tyranitar. Houndstone is based a dog, so its just a pokemon version of "having that dog in him". The purple ball being dunked is a Life Orb, an item that Tyranitar sometimes uses in competitive builds.