Few pointers that are purely objective,
If you're doing PvP you need a viable provably fair system in place with an external source of random.
This can be accomplished by drawing the winners either from random.org tickets, or unmined bitcoin / a different blockchains block.
You'd have to show proof of using X random source when a player joins, i.e creating a random.org ticket beforehand or using a chosen unmined block's hash to draw the result.