Why does negating Lady Assailant of Flames' effect still require banishing cards?

Question

While playing Yu-Gi-Oh! (via Duel Links), my opponent had Lady Assailant of Flames face down. Its text reads as follows:

FLIP: Remove 3 cards from the top of your Deck from play to inflict 800 points of damage to your opponent's Life Points.

I attacked it face down, which required it to flip face up. However, I attacked it with Element Saurus that had its negating effect active (I've bolded it below):

This monster gets the following effect(s) while there is a monster(s) with the following Attribute(s) on the field:
● FIRE: This card gains 500 ATK.
● EARTH: Negate the effect of an Effect Monster that this card destroyed by battle.

The end result was the following:

1. Element Saurus declares an attack
2. Lady Assailant of Flames flips
3. The top three cards from my opponent's deck are removed from play (i.e. banished)
4. The animation plays for an effect being negated and no Life Point damage is dealt
5. Lady Assailant of Flames is destroyed

I was really surprised that Step 3 happened, and I would have expected that to be negated too (I would have expected it to not remove the cards nor inflict damage). Why does negating Lady Assailant of Flames' effect still require banishing cards?

Answer 1

As the only time this card was released was back in 2003, it is using an older wording standard. This effect can be broken up into two pieces:

Remove 3 cards from the top of your Deck from play

and

inflict 800 points of damage to your opponent's Life Points.

The key point of this effect is that it uses the word "to," which was the old way to indicate a cost. "[Do X] to [Do Y]" - X is the cost, and Y is the effect. Modern cards use a semi-colon instead of the word "to" to make a cost more explicit. If this card were re-released, its text would likely read like this:

FLIP: Banish the top 3 cards of your Deck; inflict 800 damage to your opponent.

(These rewordings were done using a standard Konami called "Problem-Solving Card Text": an overhaul of effect wording to help clarify scenarios like this. Specifically, see bullet point 2 under "Action Structure" of this page for the guideline that relates to identifying costs)

When an effect is negated, paying its costs are not (see Activation Cost, paragraph 4), . Since this card does not use wording that implies using this effect is optional (such as "You may remove 3 cards...", see paragraph 3 of that previous link), the effect must be activated and its costs paid unless it is impossible to pay the cost (such as if you had less than 3 cards in your deck). Element Saurus then negates only the effect part.