If you control "Blade Knight" and a face-down monster on your side of the field, "Blade Knight"’s second effect is not applied because you control another monster (whether it is face-up or face-down is not important).

If you have two "Blade Knights", then their second effects are not applied because for each one, you have another monster on the field besides the "Blade Knight".

If "Blade Knight" destroys a Flip Effect Monster like "Slate Warrior", even that monster’s non-Flip effects are negated. So in this case, "Slate Warrior" does not reduce the ATK and DEF of the "Blade Knight" that destroyed it, because "Blade Knight" negates its effect.

If "Blade Knight" destroys "Spear Cretin", "Spear Cretin"’s effect is not applied.

If "Blade Knight" destroys "The Immortal of Thunder", its effect is negated. If your opponent had already gained the 3000 Life Points, then your opponent does not lose the 5000 Life Points. If "Blade Knight" attacked "The Immortal of Thunder" while it was face-down, your opponent neither gains nor loses Life Points from "The Immortal of Thunder"’s effect.

The effect of a Flip Effect monster destroyed by "Blade Knight" is negated while the destroyed card is in the Graveyard. If the monster is Set again on the field, then the Flip Effect is activated when it’s flipped again.

If "Blade Knight" attacks a face-down Attack Position Flip Effect Monster with equal ATK, and both monsters are destroyed, then "Blade Knight"’s effect is applied because it destroyed the monster, and the monster’s effect is negated.

Divine Wrath: You cannot chain "Divine Wrath" to Continuous Effects such as:"Blade Knight" (either effect)

Pole Position: I have "Pole Position", "Blade Knight" (1600 ATK / LIGHT), and "Luminous Spark" (+500 ATK to LIGHT) face-up on the field and 2 cards in my hand. The opponent has "Giant Orc" (2200 ATK / EARTH) face-up on the field, which is the highest-ATK monster on the field. If I Set 1 of the 2 cards in my hand, "Blade Knight" gains +400 ATK with its effect, becomes the highest-ATK monster, and because of "Luminous Spark" an infinite loop is created. So I am not allowed to Set a card.

Pole Position: The opponent has "Blade Knight" (1600 ATK) equipped with "Butterfly Dagger - Elma" (+300 ATK; 1900 ATK total) and 2 cards in hand, along with "Marauding Captain" (1200 ATK). The turn player has "Robbin' Goblin", "Pole Position", and "Giant Orc" (2200 ATK). The turn player attacks "Marauding Captain" with "Giant Orc", inflicting 1000 points of damage. The opponent has to discard a card because of "Robbin' Goblin" and an infinite loop is created because "Blade Knight" now fluctuates between 2300 and 2000 ATK (either above or below "Giant Orc", making it the strongest monster on the field or not). Therefore, "Pole Position" is destroyed.