I had my eyes on Contagion Engine as a card that was spiking in price, though Spike Weaver decided to spike harder and disappear off of the internet this week.

I would imagine that new demand is due to the same cause as the Contagion Engine spike- Atraxa, Praetor's Voice. The Commander spikes are showing no sign of stopping, and I expect to see more and more throughout the week. I'll admit to not being the most knowledgable on the Commander format, though as we see more and more proliferate-based buyouts, I believe that Inexorable Tide is looking like a great penny stock.

The Modern Masters reprint definitely increased the quantity of these that there are in the wild, though there aren't a ton of listings as of now, and it plays great in a deck focused on proliferating counters, for obvious reasons. The card has seen some small growth, and I expect this to continue.