Fluid Fugue - Mugic Ruling

Since you've did the work and found the section in the comprehensive rules, you're right haha

If the intent were for the target creature it should have said "the target creature gains "

Well, thanks
That's what I was thinking, I just wanted another opinion.

here's where your not quite right, the mugic does have poor wording but the "that creature" does refer to the target not the caster.

the quote your using is for if no creature is specified on the mugic at all but since the mugic does specify a target that target is what is referred to with "that creature"
the quote your referring to is for mugic and abilites with no clear target for example if you wanted to you could reword battlesong of renewal as "this creature heals 25 damage" just like the original wording of song of resistance but you could NOT just write "that creature heals 25 damage"  because "that" is used to cover an already specified target.

for your example m'arrillian this is how you would word a mugic that intedend to give he caster another mugic
"if the caster has caster this mugic cost   instead" or "if the caster has water it gains  "

this card is just like another card in the cycle sonata of storms the target gains all the effects. its more clear on that card since the target would probably want both effects.

After another complete revision. I tried to make some comparisons with the other cards from the same set.

By looking at Sonata of Storms, a Mipediam Mugic with cost 2, it says :

«Target Creature gains "Range" and "Swift 3." If the caster of this Mugic has Air, that Creature also gains "Invisibility: Surprise."»

There is also anothr Mugic that cost 2 mugicians from the danian tribe Rocky Refrain:

«Target engaged Creature gains 5 Energy for each Elemental Type the opposing engaged Creature has. If the caster of this Mugic has Earth, the target Creature gains an additional 5 Energy for each Elemental Type the opposing engaged Creature has.»

Consuming Cacophony was the other Mugic but from the Underworld tribe that deals 30 damage if the caster has fire.

By these comparisons and the fact that the mugic has a target. Thanks to Chidosin, I'm pretty confident to say that I was wrong indeed, but that the creature gaining the Mugic is the targeted creature.

Thanks again Chiodosin, you made me do some more homeworks

That's interesting. I always played it with the caster gaining the mc oops haha
Thanks Chiodosin