What used to turn Cherrim into its Sunshine form?

Question

Generation IV
During harsh sunlight, Flower Gift increases the Attack and Special Defense stats of the Pokémon with this Ability and its allies by 1.5×.

Flower Gift is not responsible for changing Cherrim from Overcast Form into Sunshine Form.

Flower Gift can be copied by Trace or Role Play.

Source

If Flower Gift didn't turn Cherrim into its Sunshine Form in Gen 4, what did?

Comments

https://replay.pokemonshowdown.com/gen4doublesou-1215914200
It didn't turn without the ability idk

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Does Cherrim have it's Sunshine Form im Diamond? I have a Cherubi that I can grind some levels on and test some things out.

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It definitely has a Sunshine form in gen 4, I've seen sprites and it has a Bulbapedia page

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It might be Flower Gift that changes Cherrim's form, IDK.
However, it can keep its sunshine form even if it loses Ability, but that's only after Sunny Day is out, as shown in this replay:
https://replay.pokemonshowdown.com/gen4ou-1215944824-z8f0vraxew35hmru7x0b5gnq8p6t24xpw

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This might be a Showdown! bug. I'll try asking on Smogon.

Answer 1

In Generation 4, Cherrim used to transform to it's Sunshine during Sunlight (weather) in battle, without the influence of Flower Gift. This means, in that gen, Cherrim was able to transform even without that ability. It was from Gen 5 Cherrim began to transform using Flower Gift.

(Proof : Using a manipulating software, change the ability of Cherrim in any Gen 4 game. Enter it in a battle and use Sunny Day to activate sunlight. See what happens. Do this in any other Generations. You will find that it won't happen!)

So, Sunlight alone was the cause of transformation of Cherrim in Gen 4

Source #1 : My experience
Source #2