The player may pay 3 and tap Horn of Gondor to make as many 1/1 creature tokens as Humans under the player's control, meaning the player's total number of Humans will double every time, barring removal and creatures dying in combat
Until then, its good
The commitment of a one mana spell might be low enough that a deck that wants to go for that as an endgame option could actually come up at some point in the future if theres a deck that wants enough of the temporary exile effects anyway
Counters can be found in all colors so you can include counter abilities in any deck
In addition, several different Monsters in the Duel Monsters Spirit World Ritual Summoned (Kozaky, Skull Knight, Skilled White Magician and Skilled Dark Magician)
Disdainful Stroke was already a strong sideboard option, but the rise of this archetype makes it even more important, and I expect to see the Malevolent Hermit / Disdainful Stroke balance move back towards the instant