Minecraft wiki entry for Thunderstorm, associated text: Lightning may randomly spawn a "skeleton trap" horse with a chance of 0.75–1.5% chance on Easy, 1.5–4% on Normal, and 2.8125–6.75% on Hard, depending on the regional difficulty. A player triggers the trap by moving within 10 blocks of the horse, whereupon the horse transforms into four skeletal horsemen. A non-triggered trap horse despawns after 15 minutes.
A pig struck by lightning turns into a zombified piglin.
A creeper becomes charged.
A villager gets replaced by a witch.
A red mooshroom changes into a brown mooshroom and vice versa.
A lightning strike on a turtle instantly kills it, and it drops 1 bowl instead of its normal drops.[2]