Portal to Alternate Timeline

The owner of target creature permanent puts it into
their sideboard then for each permanent and/or
card placed in a sideboard this way it's owner reveals
random cards from that sideboard until they reveal another creature. Then the owner of each creature
puts those creatures onto the battle field fused
together (they are a single permanent with the
combined creature types, power and toughness, mana
value, text boxes, ect of both creatures)