Does Mystic Mine stops all monster effects? Or just activation?
It sounds like only activation, so continuous monster effects may still be active? Like Denko Sekka's effect?
If your opponent controls more monsters than you do, your opponent cannot activate monster effects or declare an attack. If you control more monsters than your opponent does, you cannot activate monster effects or declare an attack. Once per turn, during the End Phase, if both players control the same number of monsters: Destroy this card.
Cannot be Special Summoned. While you control no Set Spells/Traps, neither player can Set Spells/Traps nor activate Spell/Trap Cards that are Set on the field.
Another similar case would be Mystic Mine vs Majesty's fiend, will Majesty's Fiend effect will be active?
Cannot be Special Summoned. Monster effects cannot be activated.
Another case would Majesty's Fiend vs Denko Sekka, will Denko Sekka's effect by active?