Unfortunately, thanks to The Maths TM, it only upgrades most creatures for a narrow range of levels. It’s a rank 5 spell, so only level 9 and higher parties can use it, but animal form can only be heightened to a max of rank 5 so most of the stat changes are static.
Nearly everything benefits from becoming huge, gaining 15 foot reach, and gaining 20 temp HP.
The only non static change, AC = 18 + level, will give a monster an AC of 27 when the caster first casts it at level 9, which is high for a PL-2 monster, but only moderate for PL+0 and low for PL+1. Once the caster is level 12 it gives an AC of 30, which again is high for a PL-2 monster, but low for PL+0, and always a downgrade for PL+1 or higher monsters. By level 15 it’s an AC of 33, which is low for PL-1 monsters. It’s always monsters weaker than the party that will benefit the most from it, but they generally have to be so much weaker than the party that it’s not actually worth spending a spell on them.
Attack modifier +18 is amazing for creatures under level 5, but that’s so low I’m not sure they award experience to a level 9 and higher party. For monsters between levels 6-10 it might be an upgrade, but once the creature is level 11 it’s always a downgrade.
4d8+7 damage is much swingier than most damage, but with an average of 25 it really starts to drop off once a monster is level 12 or higher. With a max of 39 really good rolls can just about keep up with level 13 damage (3d8+14), but even then most monsters would prefer the guaranteed +7 rather than the chance to roll an extra 8.
Lastly, the +20 acrobatics is extreme for a level 7 creature, but moderate for level 9 and low for level 11, so its usefulness quickly diminishes.
If you can get the player to cast it on a much weaker monster as soon as they get it it’s worth choosing the fail the save, but a single creature has stats roughly of a PC 4 levels higher than them, so it’s overwhelmingly more of an upgrade for PCs than monsters.
Unfortunately, thanks to The Maths TM, it only upgrades most creatures for a narrow range of levels. It’s a rank 5 spell, so only level 9 and higher parties can use it, but animal form can only be heightened to a max of rank 5 so most of the stat changes are static.
Nearly everything benefits from becoming huge, gaining 15 foot reach, and gaining 20 temp HP.
The only non static change, AC = 18 + level, will give a monster an AC of 27 when the caster first casts it at level 9, which is high for a PL-2 monster, but only moderate for PL+0 and low for PL+1. Once the caster is level 12 it gives an AC of 30, which again is high for a PL-2 monster, but low for PL+0, and always a downgrade for PL+1 or higher monsters. By level 15 it’s an AC of 33, which is low for PL-1 monsters. It’s always monsters weaker than the party that will benefit the most from it, but they generally have to be so much weaker than the party that it’s not actually worth spending a spell on them.
Attack modifier +18 is amazing for creatures under level 5, but that’s so low I’m not sure they award experience to a level 9 and higher party. For monsters between levels 6-10 it might be an upgrade, but once the creature is level 11 it’s always a downgrade.
4d8+7 damage is much swingier than most damage, but with an average of 25 it really starts to drop off once a monster is level 12 or higher. With a max of 39 really good rolls can just about keep up with level 13 damage (3d8+14), but even then most monsters would prefer the guaranteed +7 rather than the chance to roll an extra 8.
Lastly, the +20 acrobatics is extreme for a level 7 creature, but moderate for level 9 and low for level 11, so its usefulness quickly diminishes.
If you can get the player to cast it on a much weaker monster as soon as they get it it’s worth choosing the fail the save, but a single creature has stats roughly of a PC 4 levels higher than them, so it’s overwhelmingly more of an upgrade for PCs than monsters.