Psalm 130
When reciting Psalm 130 after Yishtabach during the Ten Days of Repentance, it is customary in some communities to open the ark and recite the verses responsively after the Chazzan. The Chabad custom, however, is to recite it but not responsively, and the ark is not opened.
No Hallel
Hallel is not recited on Rosh Hashanah and Yom Kippur because these are days of judgment.