See FreezeBurnParalyzeEffect in the pokered assembly at src/engine/battle/core.asm.
cp a, PARALYZE_SIDE_EFFECT1 + 1 ; 10% status effects are 04, 05, 06 so 07 will set carry for those
ld b, $1a ; 0x1A/0x100 or 26/256 = 10.2%~ chance
jr c, .next1 ; branch ahead if this is a 10% chance...