Timeless Ascendancy

Proliferate isn't actually that effective for the Calendar, as it only gives you +1 counter. You can achieve that by just untapping something normally. The best way to get counters on the Calendar is via doubling effects or by its own ability. You also want to have a way to get to the Calendar as fast as possible, cause without one the deck essentially doesn't do anything. Ideally this would mean running Urza's Saga, but it's very expensive. Alternatively, you could run Trinket Mage, which would also let you run Voltaic Key so you can reuse Calendar's doubling ability. You'd also want cards like Kiora's Follower (same reason), which not only lets you reuse the Calendar but gives you a tap that doesn't require an attack, putting more counters on the clock. Seedborn Muse works like a charm in the build, as it will untap all your stuff, giving you another full turn of tap shenanigans, which essentially halves the amount of time you need to build the Calendar to a win.