Do deliberate sexual fantasies without physical practice constitute masturbation necessitating a ritual bath (ghusl), and are the resulting transparent white discharges considered semen (maniy)?

Praise be to Allah, who has accepted your repentance for the forbidden act of masturbation. We advise you to stop recalling fantasies, to complete your repentance and to close a door through which Satan might enter. Guarding one's thoughts is among the most important things for one who seeks Allah Almighty, so be keen not to think about anything except what benefits you in your religion or your worldly life. As for the mentioned fluid, it appears to be madhy (prostatic fluid), which necessitates ablution (wudu') and cleansing whatever it touched of the body and clothing.