Hello,

The buildings have a larger hitbox, so they're not far enough to hit his hitbox. If you have lane control (a tower down) and the RG is placed on the lane you had destroyed, you can push him with Cannon, etc.

However, the only buildings that can force him to retarget those buildings when no towers are down are Tesla and Tombstone, as they are smaller than the other ones.

You could also use one of your troops to push the RG out of range of the arena tower, so he will target the other building you just placed down.


I didn't find the right solution from the internet.
References:
https://forum.supercell.com/showthread.php/1381900-Clan-Chest-Update%21%21%21%21-Legendaries
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