There are a ton of fascinating cards in Magic: The Gatherings Tarkir: Dragonstorm set and the best part of them is that a good number of those cards combo off with other Magic cards
Dont expect Umbral Mantle to stick around very long in most Commander games, but if your opponents are light on artifact removal, things could get very interesting
For example, if its discard, countered, or destroyed, its put into your graveyard, remaining in the game
It has a very low casting cost, it's a token maker, and it can add counters on any permanent
This is especially good alongside Awaken the Woods, which makes land-creature tokens
If you time these correctly, you can get the most benefit from cards like Merlin Goat who grants one free Lore when entering play