Grand Ossuary

You choose the number of target creatures and declare how you are distributing the counters as you put the first ability on the stack. Each target must receive at least one +1/+1 counter.

Any target that is illegal when the first ability resolves won’t get any +1/+1 counters. Those counters are essentially lost; you won’t get to put them on another creature.

For the chaos ability, the total power of the creatures a player exiled is the total power of those creatures as they last existed on the battlefield, including any bonuses from +1/+1 counters, Auras, Equipment, and other applicable effects.