Put Diregraf Colossus into play by itself, it stays a 2/2. Put it into play with ONE other Zombie, it becomes a 5/5. Put it into play with TWO other zombies, it stays a 2/2. I believe it triggers correctly when reinforced from hand regardless of the number of Zombies in play, but I’m not sure.
This has been acknowledged by JC and he said it wasn’t an unintended change. So hopefully a fix by next patch.
I confirm the above. Rather annoying…
Just opened a Diregraf Colossus, when it comes into play it stays a 2/2 regardless of how many other zombies are in play. Its ability only triggers when a zombie comes in AFTER it is on the board. This is a bug, right?
Yep. Second post in this thread. 
It does work correctly with 1 zombie in play. And will continue to work correctly as you play more zombies. It’s a bit annoying but it’s how I’ve been using it for now.