Using Parallel Universe on a swarm of Scarabs currently produces some rather interesting and often overpowered effects. It is debatable whether this is actually a bug but it could be so easily abused it might need to be changed anyway. These screens are all taken from AI matches so there's no desynching involved or anything.
Here's two Scarabs. They've been through a lot so their stats might not be what you'd expect from just two Scarabs, but what's important is that the number of Scarabs on the field has not changed yet this turn.
After using Parallel Universe and before ending the turn, all is as it should be.
Aaaaand we have a problem. The Scarabs on the right are fine; they gained +0/+1 as they should since a new Scarab came into play. The leftmost Scarab, however, entered play that turn, saw that there were two Scarabs already on the field, and gained +0/+2 accordingly. I've seen this happen with many Scarabs on the field, and each time, the new Scarab's HP increases by the number of existing Scarabs (like a freshly played Scarab) rather than by the number of new Scarabs on the field (like any Scarab that was present before the start of the turn).
Perhaps this is intended, perhaps not... but if I were to say, have five Scarabs on the field and duplicate one, that new one would immediately gain +0/+5, even though the Scarab it was copied from already had +0/+4 added to its stats for the "Scarabs on the field bonus". Let's do some math:
Turn 1: 4 scarabs at 3/5 (not unusual, they all ate one creature), one is duplicated
Turn 2: 4 scarabs at 3/6, one at 4/10 (say it ate something), that one is duplicated
Turn 3: 4 scarabs at 3/7, one at 4/11, one at 4/15, duplicated again, another Scarab is played as well
Turn 4: One scarab at 2/8, four at 3/8, one at 4/13, one at 4/17, one at 4/22
See why this is scary?