The Physical/Special Plit didn't mean a lot of changes to entei, since it's main attacks are Fire Blast/Solar Beam/Double-Edge, who keep being the same kind of attack.
But this generation Entei got Will-o-Wisp, Powerfull Herbed Solar Beams and Life Orbed Double-Edge, letting it burn Physical sweepers, catch Bulky Waters off guard and 2KO Blissey.
In other hand, Entei is outclassed by others Special/Mixed sweepers, have a bad time switching on SR and is owned by a lot of OU sweepers such Gyarados, Tyranitar, Garchomp, Salamence, Electivire, PorygonZ...
In summary, Entei became an okay BL Pokemon