If a monster is unaffected by Spell Cards, that only applies to the monster. It does not apply to a player. For example, if "Snatch Steal" is equipped to a monster that is unaffected by Spell Cards, control of the monster will not switch but the opponent will still gain 1000 Life Points during each of their Standby Phases. Nor does it apply to something like "Metallizing Parasite - Lunatite", which would still be destroyed instead of the equipped monster, even if the monster itself was unaffected by Spell Cards.
If a monster is unaffected by Spell Cards, that extends to any attacks the monster makes. A monster unaffected by Spell Cards can attack while "Swords of Revealing Light" is active, and its controller will not have to pay for "Toll" or "Gravekeeper's Servant" in order to attack with it. It can also ignore the effects of "The Dark Door" or "Vengeful Bog Spirit".
Spell Card effects can still be applied to monsters that are unaffected by Spell Cards, but their effects will simply disappear. It’s like there’s a force field surrounding the monster, protecting it from the Spell Card’s effect. However, the Spell Card still "sees" the monster and may attempt to apply its effect on the monster.
- Example 1: A player has "Horus the Black Flame Dragon LV6" and "Blue-Eyes White Dragon" on the field and the opponent activates "Fissure". The effect of "Fissure" looks for the lowest ATK monster, and attempts to destroy "Horus the Black Flame Dragon LV6", but that monster is unaffected by Spell Cards and isn’t destroyed, and the effect of "Fissure" just disappears. "Fissure" does not "skip" "Horus" and try to destroy "Blue-Eyes" instead.
- Example 2: The opponent controls "Silent Swordsman LV5" and "Gemini Elf". The turn player controls a "Sheep Token" and activates "Creature Swap". When "Creature Swap" resolves, the turn player selects his "Sheep Token" to give to the opponent. The opponent can select "Silent Swordsman LV5" for the effect of "Creature Swap". However, since that monster is unaffected by Spell Cards, the force field around him nullifies the effect of "Creature Swap", and no monsters change sides. (Note that this is very different from monsters that cannot change sides, like "Mataza the Zapper" or "Blindly Loyal Goblin". These monsters cannot be selected for "Creature Swap" and another monster must be selected instead.)
Here is a list of cards that allow or are Unaffected by Spell Cards: