If you mutate Gemrazer onto Nexus, it still mutates when Nexus stops being a land at the end of the turn
And on top of that, you can trigger his ability at instant speed
[Copy Editors Note: Hey, I resemble that remark!] One of my first control decks, named The Masterpiece by Michael Flores, was a four-color monstrosity that solely generated card advantage from this enchantment
Whether you're using it to catch up with a breakaway green player on a ramping rampage, or to save yourself after some disastrous missed land drops, getting the effect of this pegasus is always going to feel good
MDFC lands are deceptively powerful, allowing you to increase your number of lands in a Commander deck, or your EDH deck's removal count at the same time