in its mana cost, X is considered to be 0.Helm of the Host creates a token copy of its equipped creature at the beginning of combat on your turn. The token is not legendary and gains haste, allowing a deck to duplicate a commander or powerful creature without immediately losing a copy to the legend rule. The tokens remain after combat, so repeated turns can build a substantial board.
Godo, Bandit Warlord provides a specific combo. With Helm attached to Godo, each combat can create a new hasty Godo token. When that token attacks for the first time that turn, its ability untaps it and adds another combat phase. The next combat can create another fresh token, allowing the process to repeat while the setup remains intact and the new tokens can attack.
Outside that combination, creatures with entry abilities provide immediate value from the copies. Eternal Witness can recover another card, while a copied creature with a continuing static or triggered ability can strengthen the whole board. Helm also works on nonlegendary creatures, so its value is not restricted to commanders.
The mana investment is substantial: Helm costs four to cast and five to equip through its normal ability. Equip timing also usually limits attachment to your main phase with an empty stack. Removing the equipped creature or the Equipment can stop future copies, and a creature that enters after the beginning of combat has passed will not generate a missed trigger. Build around a target whose copies justify that setup rather than expecting the artifact to provide immediate value on an empty board.
