The Fusion Cores in Halo 2 looked neat and clean, with gold and brown colors. It looked more like an old ancient device than a modern plasma container. It was later when the fusion core was redesigned, in Halo 3 the fusion Cores looked more modern with the little warning stamp.The Fusion Cores can be moved, but be aware to damage it and turn the core light into red. One explosion is enough to kill anyone nearby.
As mentioned above, the Fusion Cores are basically explosive barrels. So its presence in some multiplayer maps is extremely useful if exploited well. If a non-experienced player is seem to be hiding behind one of those dangerous plasma containers, then aiming at it is a one-shot kill if done well too. Some players just use it for bare fun, one example is stashing it under a vehicle and blowing it up, resulting in either the vehicle being thrown in air or simply explode. If one barrel or container is exploded, the one beside it well also explode, triggering a chain explosion.