Slickshot Show-Off is a Bird Wizard.
The text of Wizard's Lightning reads "This spell costs 2 less if you control a Wizard."
Therefore, with a Slickshot Show-Off on board, Wizard's Lightning should cost R, not R2.

I plotted Slickshot Show-Off on turn 2 and summoned it on turn 3, intending to follow up Wizard's Lightning with additional spells that turn.

To my horror, all 3 of my mana went to Wizard's Lightning instead. (Log attached.)

I chose to continue, and my opponent removed the first Slickshot Show-Off on their turn.
But on turn 4, I drew a second one, which I chose to hard-cast this time.
On turn 5, I drew another Wizard's Lightning, which showed the alternate casting cost correctly.
But, when I played it, 3 lands were tapped instead of only 1.
At this point, I was out of gas and had to concede the match.

Meanwhile, both turns where I cast Wizard's Lightning, my opponent had only an Esper Sentinel and Innovative Metatect, and lands to cast them on board. (Both times, Innovative Metatect was the target of Wizard's Lightning.)
Other than the Portable Holes used to remove my Slickshot Show-Offs, nothing else was played before the final turn, where I stopped paying attention and conceded.

None of these cards alter the casting cost of Wizard's Lightning or the creature type of Slickshot Show-Off.
Therefore, I believe this is a bug. Please correct. Thanks.