Drumbellower gives your creatures another untap during every other player's untap step. In multiplayer, that can make a single round contain several opportunities to reuse mana creatures and tap abilities. It also lets creatures attack on your turn and become available to block before the next opponent's main phase.
Mana creatures benefit when the deck has instant-speed spells or activated abilities to spend the mana on. Mother of Runes and similar protective creatures can become available again for another opponent's turn, while creatures with useful tap effects can contribute repeatedly. The card is most productive when untapping has a purpose beyond merely straightening creatures that were not going to do anything.
It does not grant flash to spells, so untapping a mana creature on an opponent's turn does not let you cast a sorcery-speed creature then. It also does not remove summoning sickness. A creature that has not been under your control since the beginning of your most recent turn still needs haste to use a tap-symbol ability. Flying gives Drumbellower a modest combat role, but its main value is multiplying the work done by the rest of your board. Three mana makes it easy to fit into creature-based value decks, especially those with many activated abilities. Keep enough interaction to preserve the useful creatures around it. Untapping an established engine several times can be excellent; untapping a board with no relevant actions does not by itself create more resources.
