Once Main Phase 2 (or Main Phase 1 if no Battle Phase was conducted) has been completed, the player proceeds to the End Phase (エンドフェイズ, Endofeizu). Any card effects that resolve in this Phase now take effect, such as "Change of Heart" or "Brain Control". The Turn Player gets to decide in which order any effect they own resolves. In addition, the Turn Player may also have to pay maintenance costs for cards such as "Clear World".
If the Turn Player has seven or more cards in his/her hand at this time, he/she must discard to the Graveyard cards until they have only six cards in their hand. This action is the very last thing to happen in any End Phase.
If an action is to be taken "at the end of the End Phase", such as the wear-off of the temporary 3000 ATK boost of "Theinen the Great Sphinx", it is, predictably, the very last thing to happen in this Phase before the Hand Limit Discard occurs.
The End Phase is the only phase that cannot be skipped by a card effect, unless the entire turn gets skipped.