You may change any number of the targets, including all of them or none of them
Under Pale Moon, it becomes trivial
The desire to explore this deck was cemented when the excellent Twitter account RosewattaStone posted its wonderful garbled mistranslation of the card

Amped Raptor Ancient Den Arcums Astrolabe Birthing Pod Blazing Shoal Bridge From Below Chrome Mox Cloudpost Dark Depths Deathrite Shaman Dig Through Time Dread Return Eye of Ugin Field of the Dead Fury Gitaxian Probe Glimpse of Nature Golgari Grave-Troll Great Furnace Grief Hogaak, Arisen Necropolis Hypergenesis Jegantha, the Wellspring Krark-Clan Ironworks Lurrus of the Dream-Den Mental Misstep Mycosynth Lattice Mystic Sanctuary Nadu, Winged Wisdom Oko, Thief of Crowns Once Upon a Time Ponder Punishing Fire Rite of Flame Seat of the Synod Second Sunrise Seething Song Senseis Divining Top Simian Spirit Guide Skullclamp Summer Bloom The One Ring Tibalts Trickery Treasure Cruise Tree of Tales Umezawas Jitte Underworld Breach Up the Beanstalk Uro, Titan of Natures Wrath Vault of Whispers Violent Outburst Yorion, Sky Nomad If youre newer to Modern, you may not be familiar with the banlist or the cards on it

Therefore, if "Mew ex" ( Mythical Island ) uses "Genome Hacking" to copy such an attack, it can do so without discarding any Energy, as long as none of its attached Energy matches the type specified by the copied attack
But they are stuck in the pipeline now