I have ... no idea whatsoever you are talking about.
what do you mean by 'placed them on platforms'. also, if you've already placed them on platforms, doesn't that imply your enemy is on its own platform?
I assume you have variables for its position and velocity that you update at regular intervals (Swing Timer) - in which case just add a fixed amount to the (downwards) vertical velocity component on each update. This will result in the downwards speed increasing steadily - just like g.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...