I have a "weird" looking concept. if the game is very four colors it might not be suitable.
Ions ago, in a far off in a galaxy, a planet in which life never evolved beyond the celular level. High complexity was acquire at the cellular level, communication, the key feature for organized life form was born.
But the most evolved creatures in this world still looked very similar to a Paramecium. This predatorial species lived peacefully, until one day, disaster occurred. Attacked by aliens who wanted to turn their world into planet-wide mining facility, these creatures fought fiercely for their survival. But without any kind of technology, these beings didn't stud a chance. As their enemies started converting the planet into a life devoid mine, the remaining creatures sneaked into enemy ships. From the inside, they destroyed the cruisers, and attached their spores into the pieces of the wreckage. Disaminating like pollen in the wind, the spores dispersed to the universe.
Today, Earth:
A meteorite hits a farmer's granary. But it was not a meteorite, it was a fragment of a spaceship. Most of it got eaten away in the stratosphere, but some survived. The farmer was lucky to be off harvesting, as the explosion made a huge crater. As the man explored the site, he found a ball, a brown ball, the size of a baseball. It's exterior had been burned off in the atmosphere, and as the farmer peeled it, he found what he thought was a seed. Knowing his trade, but not caution, the man put the ball in a bucket of water. In awe, he looked as the ball started to crack, freeing a yellow goo. Quickly, the goo absorbed the water. As it made it's way out of the ball and hydrated, the farmer could see other balls and "organs" inside. It was the size of a dog, yellow and covered with hair like appendices. Several balls and stuff floated inside of it. Four of them where predominantly big, and glowed blue. Sensing another life form around him, the creature's nucleus glowed. Inside his head, the farmer could hear the creature's voice.
"Hello! We guess we made it to somewhere humid enough! We are Paramax, nice to meet you!" immediately, the thing attached to the farmer's leg. Passed the initial repulsion, the farmer made friends with the alien, who proved useful in eating away everything inside the crater, and cleaning up the mess. It seemed to be able to phagocyte everything and assimilate it, so it was easy for the farmer to rise the little guy.
Paramax's particular biology could prove useful in the fight against crime, now that he was big enough. As ambassador for his species, Paramax thought that making a good name for himself, would make the humans prone to accepting his kind in this world. As far as he knew, he might well be the only survivor. But replicating and invading this planet would be as bas as what those other aliens did to his world, so Paramax set off with a quest, to prove humans how marvellous it would be to be neighbours!
So build-wise, this thing would be absorbing energy and hits, and regenerating; hard to kill in resume. He'll have only a few attacks, like engulfing prey, or perhaps a telepathic attack. He's blind and mute and can only communicate mentally. Again it's a weird concept but I think it would be fun.