The reality all beings in Equestria experience doesn't exist unless a pony has their cutie mark.
Until a pony with that cutie mark does show up, creating or manipulating or even interacting with whatever it is, is far more difficult than it would be in a regular reality.
The hard physical properties is determined by how many cutie marks across time and space and the degree of expression any one pony achieves.
The more successful or wide spread the more easily it is to utilise the flank power representation.
Consider Twilight Sparkle and the magic of friendship, the first act is creating a friend. That being Spike the dragon, for an impossible test.
Once Twilight Sparkle did that friendship has a physical and metaphorical anchor to exist in the past and in the future.
Fact is once a pony's flank is near by the act of doing similar feats is eased, usually. The closer a pony is to the flank power the less intensive it is to have the specific flank exist.
Sweetie Bell burned the juice. There's more cutie marks of anything else other than cooking juice and that being poured in a glass. A being in Equestria has to connect at least a little to the correct or similar flank to bring the desired result.
Sweetie Bell, reached for other adjacent results.
In Applejack needs a naptime she makes baked bads. A failure to connect to the appropriate flanks.
The common method of connecting to those flanks is knowledge transfer.
>Prove pony flanks do make up the world.
Every other creature and the area they live in is nigh impossible for themselves to change. The effort needed to connect to a flank to make it be is incredibly huge for those without a flank in the game.
<Zebra proto-cutie mark
By mimicking flanks they can more easily tap into other flanks.
<Villains
They all have different ways of tapping into flanks.
That is how they can enact what they do. It's also why they lose, because they don't got no flank or are out numbered by flanks.
Which brings us to the Bad Deserted Timeline, flanks are disconnected making the effects also disappear.
This almost occurs in Starlight Glimmer's town, only kept afloat by the cutie marks being in storage and being in Equestria home of the flanks.
This is why the elements of harmony sent Nightmare Moon to the moon, being separated from other flanks makes anything and anybody weaker.
The flank connection and how Equestria exists is why Discord actually has any agency and power.