Question

mirror of oath and black horn of heaven

both negate the special summon, IF my opponent use card THAT specail summon another card can i use these trap card??

Last one Dark Illusion (Negate the activation of a Spell Card, Trap Card, or Effect Monster's effect that targets a face-up DARK monster, and destroy that card.)

works only against cards that SELECT a card on my field??

I think its YES on both questions

1. Mirror of Oaths negates cards that are special summoned from the deck and Black Horn of Heaven can only negate Special Summons that do not use a chain link (like: Cyber Dragon, Guardian Eatos etc...) if a card like Monster Reborn is played to special summon a monster from either players graveyard you can't use Black Horn of Heaven.

2. Dark Illusion can only negate cards that target 1 Dark Attribute monster on your side of the field (EX: Effect Veiler, Dimensional Prison, Cais, Raiza etc...)

Just Clarifying, Mirror Of Oaths doesn't negate, it destroys. There's A difference, for example, if you Special Summon any Gladiator Beasts, they still get their effects since they were still Special Summoned.

~Anyways Other than that, I Confirm Train.