What is "Mislahle'ah [ha'Yoreh Zikim]"?
Rashi #1: He is weary of shooting Zikim of fire.
Orchos Tzadikim (Sha'ar Leshon ha'Ra DH v'Chen): It is one who speaks Leshon ha'Ra in the way of jesting and lightheadedness, i.e. not amidst hatred.
Malbim: It is one who is Mehasel (mocks or deceives) with his friend.
What are "Zikim"?
Rashi #1: Zikim are [sparks,] like "uv'Zikos Bi'artem" (Yeshayah 50:11) and Zekukim Dinor (Bava Metzi'a 85b). Malbim - they are sparks that burn garments. After, he shoots arrows - refer to 26:18:3:1.
Rashi #2: Zikim are like stones of a slingshot ("Avnei Kela" - Zecharyah 9:15), Zikasa Pasak Lan (Bava Metzi'a 93b).
What are "Chitzim va'Maves"?
Malbim: Chitzim are arrows that wound. Afterwards, he shoots Maves - arrows anointed with lethal poison, which kill.