Sending 1 card from the top of your Deck to the GY is a cost.
This card does not target.
You cannot Normal Summon or Set during the turn you activate this card, even with the effect of "Ultimate Offering".
You cannot activate "Hidden Armory" while the effect of "Dimension Fortress Weapon" is being applied.
You can activate the effect of "Red-Eyes Wyvern" during the End Phase of the turn you could not Normal Summon due to the effect of "Hidden Armory".