Invisibilty slider

I have been adding spell effects after a spell has been used, I lay the effect over the creatures then click on each creature to put them on top of the spell then update so everyone can see the effect then pull the effect and update again. This way it looks like bam a spell went off for a second and then its gone. The problem im having is there are 2 options for adding images as a creature file: visible or invisible. Now if there was a slider to go from complete invisible to complete non invisible then i could add a spell effect overlay over some creatures and they could still be scene through the spell effect, no clicking to bring 1 over the other etc.

So can we get a slider added to the invisible to say 50% and 25% visible.

Thanks

 

I wanted to add few more things to this request that has become apparent while gaming. With the use of a slider creatures behind obstacles become apparently harder to hit. At 50% transparecy they gain a + on their AC and at 25% they have a greater + on their AC. We cold also use the slider for differant forms of undead like undead, etc.

Just throwing some other ideas out there that can be used for effects with a transparency slider.

Thanks