Certainly, the easiest method to farm endless life in the first part of the Crash Bandicoot is in the "Castle Machinery" level on the third island. You can only reach this level at the end of the game, but you can get a life of 30 at a hit and simply restart the level four times to make the 99 lives.
For this method you need the green gemstone. You will get this at the level "Lost City" on the second island, when you finish the level, destroy all crates and not dying.
Once you start "Castle Machinery", take the elevator behind you, bringing you up to 30 lives, which you can collect at a time. On the other hand, you can directly take the elevator to the level exit and start "Castle Machinery" again. In this way you get 99 lives in less than five minutes.
Crash Bandicoot 2: Farm 99 Lives
Also in Crash Bandicoot 2: Cortex Strikes Back, there is a very fast method, where you can farm 99 lives in seven minutes. To do this, you simply have to start the level "Bee-Having" in Warp Room 4 and go with a crash to the electric trap at the first checkpoint. Here you will find a beehive, from which infinitely bees spawn.
As soon as they appear, make a slide-tail with a circle square to kill the bees in a single hit (it may take some practice until you get the timing). Once all the bees are dead, an extra-life appears. The bees spell endlessly and always leave such an extra life. In this way you only need seven minutes until you have 99 lives.
Crash Bandicoot - Warped: Farm 99 Lives
The fastest method we've ever seen in Crash Bandicoot: Warped will give you 99 lives in about 30 minutes. Start by level 16: Sphynxinator and get a life right behind the starting point of the level. Then follow the left path to collect four more lives after the first checkpoint. Then leave the level via the Pause menu.
When you are back in the Warp Room, load your automatically created game and play the level again in the same way. You must repeat this 20 times until you have the 99 lives.
These methods have proved the fastest in the three games of the Crash Bandicoot N.Sane Trilogy.