Using illution

[HK416]

Hi there.
My friends and i playd a game (epic munchkin) and it came down to this:
Player 1 was lvl 19 (+ gear), and we (players 2-4) powered up his oponent so it was just high enoguht to beat player 1. This included pretty much alot of one-shot items, +10 humongus enchantment and 2 monsters in total.

Suddently player 1 used illution and changed the main monster wich was lvl 18+ humongus (+10), to another lvl 18 monster.

My question is all the one-shot itmes wich stats "give +1, 2 or 3" to either side, do they take any affect from this?
We (players 2-4) was offurce aginst this, and stated that the one-shot cards says on them "give bonus to the side" (on every card, i checked) of the battle, not the specific monster.
For the record, the humongus +10 says its for the mosnter, so that did 'illution' bring down.

This was a type of "20 min break to discus" kind off thing.
(In the end, we (players 2-4) did convince him that it dindt have any effect on the one-shot items.)

Sorry if im unclear on something. If something is missudnerstood, i will try my best to explain.