Update: I found a workaround. See below.
I have an iPhone 6 running iOS 8.3 and a rMBP running OS X 10.10.3.
Both machines have the latest version of Apple's Keynote app installed.
In the past, (i.e. on Mavericks) I could create an ad-hoc wireless network from my mac, connect to it using my iPhone, and control the presentation using Apple's Keynote app.
Unfortunately, with the advent of Yosemite, I find that the iOS Keynote app is now ridiculously flaky at connecting to Keynote through an ad-hoc network.
Any suggestions/fixes to this problem?
Thank you ahead of time!