Pokemon Stadium is complete fucking bullshit even if you aren't using rentals. Everything unrelated to battles is pure kino. The battles though, make it probably the single worst Pokemon game with a normal gameplay style of all time. Even in R1 you will constantly face complete bullshit and the RNG is near-constantly stacked against you. It is a hateful game that cares nothing for your time and will do anything to fuck you over. If you want to beat the whole game with rentals, good fucking luck. It IS NOT WORTH IT. Your time would be better spent doing literally anything else. Even doing nothing would be better, since at least then you wouldn't be constantly crushed by an evil computer who wants nothing but to fuck you like a 10 dollar whore in TJ and leave you crying in an abandoned alleyway 100 miles from your hotel. It is one of the most spiteful, hateful game experiences I've ever seen. All that busted RNG and bullshit combined with the fact that it is impossible to turn off move animations. Even battles you win are still wasting your time since they take so fucking long. If you're playing the games for the GB Tower and it's speedups, box management, battling a friend, minigames, the Library, etc, they are fantastic and full of charm. Just, please, for the love of god, DON'T BOTHER BATTLING. IT IS NOT WORTH THE PAIN. Just buy a GameShark or whatever and cheat to get the Dodrio Tower.
Source: Wasted at least a hundred hours of my life on this bullshit game series