Pokemon R/B/Y - Badly burned?
Rest cures status afflictions like poison, but in Pokemon R/B/Y, the Toxic (bad poison) substatus is not removed. Burn, posion, and leech seed all use the same function to substract damage from the affected Pokemon, so a burned or seeded Pokemon with the Toxic substatus active will be taking more damage progressively (as the 'Toxic counter' will also build). This bug is easier to trigger with Leech Seed, because a Pokemon can be poisoned and seeded at the same time. However, this oversight in Rest makes it possible with the burn status too.
As shown in the second part of the video, another way to inflict "bad burn" to a Pokemon is through the Hyper Beam + Sleep glitch, which was detailed here: https://www.youtube.com/watch?v=x2AgAdQwyGI.