In The Minish Cap, the RNG seed is the same every time after a hard or soft reset and gets advanced every frame on the title screen, the screen with the "press start" text. The RNG will advance in many ways, from Link's rolls to NPC movement to enemy attacks. Because of this, extended RNG manipulations are difficult, but with reliable setups, simple manipulations are possible.
For speedruns, the most common ways to manipulate RNG is slashing your sword (advances RNG once), rolling (advances RNG once), using the Boots (advances RNG four times per dust, only on boots startup) and waiting for specific cues (advances RNG depending on what is going on in the room).