This four-mana mono-green 4/3 makes every creature spell you cast with power 4 or greater cost two generic mana less, and whenever she attacks, each of those big creatures gets +1/+1 and trample until end of turn
Kefka takes things a bit further by giving you access to black in your deck, though, giving you access to creature reanimation and tutoring straight for a Niv-Mizzet to combo out quickly
Lets use spot removal as an example to demonstrate how multiplayer adjusts our card valuations
(If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.) Legendary Creature - Human Cleric Elf Tifa, Martial Artist Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.) Whenever one or more creatures you control with power 7 or greater deal combat damage to a player, untap all creatures you control
You pay all costs and follow all normal timing rules for the card played from exile with Synth Eradicator's second ability