COLLECTOR OF ENTITIES: Each time, including the beginning of the game, another friendly character is possessed by a character using the Entity Possession ability, roll 2d6 and modify Krona's indicated combat value by +2 for the rest of the game, based on the result: 2-3: Attack 4-5: Range 6-8: Speed 9-10: Defense 11-12: Damage.

If I have more than one entity possessed charater on my team and I roll two of the same stat does it get a +4 or max out at the +3?

+3 - the rule of 3 is golden yo!

Insert the normal note that the +4 still exists and could come into play under specific circumstances. If you get +4 to Krona's Attack Value and then your opponent puts a Smoke Cloud token under him his AV would be printed+4-1 and thus end up printed+3. But the maximum modification over the printed value would be limited to +3 by the Rule of Three. It can be a bit useful to have a +4 to a stat, especially if your opponent has Perplex (like the Sinestro Corps members with their special reduce stats only Perplex).

If you have 3 possessions on your team it would be very unlucky to roll the same stat all three times, as a +6 to one stat is not going to be as useful.