Mold Breaker ignores the following abillities
>Battle Armor, Clear Body, Damp, Dry Skin, Filter, Flash Fire, Flower Gift, Heatproof, Hyper Cutter, Immunity, Inner Focus, Insomnia, Keen Eye, Leaf Guard, Levitate, Lightning Rod, Limber, Magma Armor, Marvel Scale, Motor Drive, Oblivious, Own Tempo, Sand Veil, Shell Armor, Shield Dust, Simple, Snow Cloak, Solid Rock, Soundproof, Sticky Hold, Storm Drain, Sturdy, Suction Cups, Tangled Feet, Thick Fat, Unaware, Vital Spirit, Volt Absorb, Water Absorb, Water Veil, White Smoke, Wonder Guard, Big Pecks, Contrary, Friend Guard, Heavy Metal, Light Metal, Magic Bounce, Multiscale, Sap Sipper, Telepathy, Wonder Skin, Aroma Veil, Bulletproof, Flower Veil, Fur Coat, Overcoat, Sweet Veil.
Magic Guard is not on that list so Mold Breaker does not ignore Magic Guard therefore I can not give you an example of a bulky Mold Breaker using Toxic.
Source: http://bulbapedia.bulbagarden.net/wiki/Mold_Breaker_(Ability)
I Hope I helped
//Jofly