Search effects and stuff

People are still unfamiliar so I'm gonna enlighten you.

When there are no legal targets left in the deck, you cannot activate a card effect to search your deck.

Example: Reinforcement of the Army
You use it, and realise there are no more warriors in your deck. The proper procedure is to shuffle your deck, put the Reinforcement back into your hand because you are not allowed to play it in the first place and probably get a warning somewhere.

Example: Thunder Dragon
No you cannot discard that extra Thunder Dragons in your hand if there are no more targets in the deck, just for the sake of using Pot of Avarice.

Example: D Hero Malicious
No you cannot remove that lonely Malicious in your grave when there are no more in your deck to get exactly 3 Dark to summon Damudo.

But, some horrible thing may happen. Here are some scenarios.

Example: Charge of the Light Brigade
You know you have that one last Lightlord in your deck and need it badly for your sad sad Solar Recharge.
You activate Charge, mill 3, and to your horror! Your last Lightlord got milled into the grave!
No you do not shuffle back the 3 milled cards and take back your Charge because at the point of activation, there is still a legal target in the deck.

Example: Blizzard/Whirlwind
You are awesome and try to get around the effect of that face up Oppression.
You summon Blizzard and do your fancy chain block abuse to avoid Oppression only to realize you have no more target for Whirlwind.
In this case, your opponent can oppress your Blizzard since Whirlwind is not legal to be activated and there will be 'EPIC FAIL' written all over.