"Goblin" monsters you control gain 300 ATK for each "Goblin" monster you control. During your Main Phase, you can Normal Summon 1 "Goblin" monster, in addition to your Normal Summon/Set. (You can only gain this effect once per turn.) You can target 2 "Goblin" monsters you control, then activate 1 of these effects;
• Make the Level of 1 of the monsters become the current Level of the other.
• Both of their Levels become their combined original Levels.
You can only use this effect of "Goblin Biker Grand Bash" once per turn.