I was a big fan of Maul of the Skyclaves, which had a very similar feel: White equipment for three mana, attaches for free when it enters the battlefield, four mana to equip, +2 power and flying
I did Breloom because he's my favorite pokemon, mainly because it was the best pokemon I had in my first pokemon playthrough, being Emerald
The flexibility is the beauty of the mechanic, allowing you to have two different effects on the same card depending on how much mana you have
It is very good just for the fact it provides any type of energy and also has opponent damage reduction
Cards similar to Writhing Necromass include Ghoultree
1 Alakazam (7), 2 Blastoise (7), 3 Chansey (7), 4 Charizard (7), 5 Clefairy (7), 6 Gyarados (5), 7 Hitmonchan (7), 9 Magneton (7), 10 Mewtwo (6), 11 Nidoking (6), 12 Ninetales (6), 13 Poliwrath (7), 14 Raichu (7), 15 Venusaur (7) and 16 Zapdos (6)