Can a Pokemon change abilities when it evolves into its next stage? For example, can a Intimidate Growlithe evolve into a Flash Fire Arcanine? This is what happened to me, can someone please help?
During normal evolution, a Pokemon's ability will not change, with a few exceptions.
The following are the cases when a Pokemon's ability will change:
1. Both the pre-evolved and evolved forms have two distinct lines of abilities. The Pokemon will follow the line and will not deviate.
For example, Shinx, Luxio, and Luxray have line A (Intimidate) or line B (Rivalry). Intimidate Shinx will only become Intimidate Luxio; Rivalry Shinx will only become Rivalry Luxio.
2. Both the pre-evolved and evolved forms have two distinct lines of abilities, but one or both changes upon evolution.
For example, Yanma and Yanmega have line A (Speed Boost) and line B (Compoundeyes > Tinted Lens). Only Yanma with Compoundeyes evolve into Tinted Lens Yanmega.
-- Similarly, only Porygon2 with Trace evolve into Adaptability Porygon-Z and only Rock Head Rhydon evolve into Solid Rock Rhyperior.
3. The pre-evolved form has one ability, but the evolution has two. You have a 50% chance to get either ability. I can't recall an example.
4. The evolved form has one ability, which is different than what the pre-evolved form has. The Pokemon will obviously get the new ability, regardless of how many abilities the pre-evolved form has.
Duskull has Levitate, but Dusclops has Pressure. Duskull loses Levitate upon evolving.
Snorunt has both Inner Focus and Ice Body, but Froslass only has Snow Cloak. Snorunt loses its ability upon evolving.
5. A Pokemon is migrated from GBA to DS, its species gained a new ability in DPPt, the Pokemon is not fully evolved, and its evolution has two abilities. You have a chance to learn the new ability.
An example is Clefairy: in RSEFRLG, Clefairy only had Cute Charm, but in DPPt, it also has Magic Guard. When transferring over the Pokemon, it will have Cute Charm, but when you evolve it, it may learn Magic Guard (depending on a hidden personality value). However, if the Clefairy was caught in DPPt and had Cute Charm, it will only have Cute Charm; likewise, Magic Guard Clefairy will always become Magic Guard Clefable.
There is no way to alter this change; if you want a Cute Charm DS Clefable, but your Cute Charm GBA Clefairy evolves into Magic Guard DS Clefable then it will always evolve into Magic Guard DS Clefable. You can get around this by evolving the Pokemon in the GBA BEFORE migrating, since a Pokemon will not change ability unless it evolves.
Some Pokemon who learned new abilities in DPPt and cannot evolve will not change abilities no matter what. For example, Miltank only had Thick Fat in GBA, but in DS, it learned Scrappy. It can't obtain Scrappy as its ability if it is migrated.