attack power 5 or less, at least 3 or less instead of the current 2 or less.
2 or less:
Other - **Malignant Cell, *Dagger -- 2, 0 upped
Aether - N/A -- 0, 0 upped
Air - Dragonfly, Damselfly -- 1, 1 upped
Darkness - Devourer, Pest, Parasite, Minor Vampire -- 3, 1 upped
Death - Virus, Retrovirus, Vulture, Condor, Skeleton, Elite Skeleton, *Arsenic, Grey Nymph, Death Nymph -- 5, 4 upped
Earth - Antlion, Gnome Rider, Gnome Gemfinder, Graboid, Elite Graboid, Auburn Nymph, Earth Nymph -- 4, 3 upped
Entropy - Micro Abomination, Lycanthrope, Werewolf -- 1, 2 upped
Fire - Ash Eater, Brimstone Eater, Fire Spirit, Fire Spectre, Ash, Ash (up), Red Nymph, Fire Nymph - 4, 4 upped
Gravity - Armagio, Elite Armagio, Otyugh, Elite Otyugh, Graviton Fire Eater, Graviton Firemaster, Amber Nymph, Gravity Nymph -- 4, 4 upped
Life - Rustler, Leaf Dragon, Forest Spirit, Forest Spectre, *Druidic Staff -- 3, 2 upped
Light - Photon, Ray Of Light, Guardian Angel -- 2, 1 upped
Time - Deja Vu, Elite Deja Vu, Fate Egg, Fate Egg (up), Scarab -- 3, 2 upped
Water - Chrysaora, Physalia, Puffer Fish, Mind Flayer, Arctic Squid, Arctic Octopus, Nymph Queen, Water Nymph -- 4, 4 upped
3 or less:
Other - *Short Sword, *Hammer
Aether - Spark
Air - Wyrm, Firefly Queen, Elite Queen, Firefly, Blue Nymph
Darkness - Bloodsucker, Black Nymph
Death - Flesh Spider, *Arsenic (up)
Earth - Elite Antlion
Entropy - Maxwell's Demon, Maxwell's Demon (up), Fallen Elf, Fallen Druid
Fire - N/A
Gravity - Graviton Mercenary, Graviton Guard
Life - Horned Frog, Green Nymph, Life Nymph
Light - Pegasus
Time - Elite Scarab, Pharaoh, Pharaoh (up)
Water - Blue Crawler, Ulitharid
5 or less:
Other - *Dirk
Aether - Ball Lightning, Phase Spider, *Lobotomizer, *Electrocutor
Air - Elite Firefly, *Owl's Eye
Darkness - Vampire, Gargoyle, Dark Nymph
Death - Mummy, Elite Mummy
Earth - Hematite Golem, *Pulverizer, *Pulverizer (up)
Entropy - Abomination, *Discord
Fire - Lava Golem, Minor Phoenix, *Fahrenheit, *Fahrenheit (up)
Gravity - Sapphire Charger
Life - Giant Frog, Cockatrice, Elite Cockatrice, *Jade Staff
Light - Elite Pegasus
Time - Anubis, Elite Anubis, *Eternity, *Eternity (up)
Water - Toadfish, *Trident, *Poseidon
*With Flying/Animate Weapon
**Only from an Aflatoxin or Death Nymph
And of course it can be used on any creature after anti-matter (even opponent ones - so you can simultaneously restore your own life and potentially replace a dangerous skill with one they can't use), and some mutants. The only element that doesn't currently work with Butterfly Effect is Aether (unless you count PU on creatures with Butterfly Effect already). Is having 38 distinct cards (including weapons, but only one of a card and its upgrade) that can be used with Butterfly Effect just not enough? With 5 or less, almost every creature card in the game can be used (the main exceptions being dragons and aether/fire cards). If the designers had wanted a card that could be used on almost everything they would have made it that way. I think 38 options is plenty.