Yes, he's bringing up Grease again.

[Jack Napier]

I've argued before about moving creatures moving through Grease being flat-footed. Here's me using the player's guide to re-open the argument and have put the most pertinent arguements in bold type.

The Grease spell decription states:

A grease spell covers a solid surface with a layer of slippery grease. Any creature in the area when the spell is cast must make a successful Reflex save or fall. A creature can walk within or through the area of grease at half normal speed with a DC 10 Acrobatics check. Failure means it can't move that round (and must then make a Reflex save or fall), while failure by 5 or more means it falls (see the Acrobatics skill for details). Creatures that do not move on their turn do not need to make this check and are not considered flat-footed.

[Greased item stuff removed as it is not pertinent to this use of the spell]

Scott's note: The spell description, as mentioned the first time, is very vague on its own. But it TELLS YOU to see the acrobatics skill for details on balancing while moving into/through/out of this type of terrain. This explains why they would even mention "creatures who do not move [...] are not considered flat-footed" at the end.

The Rules for Acrobatics State:

Cross Narrow Surfaces/Uneven Ground [Scott's note: This is fancy wording for "Balancing"]

First, you can use Acrobatics to move on narrow surfaces and uneven ground without falling. A successful check allows you to move at half speed across such surfaces—only one check is needed per round. Use the following table to determine the base DC, which is then modified by the Acrobatics skill modifiers noted below. While you are using Acrobatics in this way, you are considered flat-footed and lose your Dexterity bonus to your AC (if any). If you take damage while using Acrobatics, you must immediately make another Acrobatics check at the same DC to avoid falling or being knocked prone.

Scott's note: The stuff in bold pretty much says it all... but also good to note is that if a creature takes damage while balancing (ie. through readied action or AoO) they must make another acrobatics check.
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So I say, based on this, moving through grease makes a creature flat-footed and is penalized as such until their next turn (as all penalties do)

You may say this makes grease more powerful than most level 1 spells... but it IS one of the best and most versatile level 1 spells; that's why I took it! (also because making creatures slip and fall fits my character's trickster flavour.)

However, consider the following: Creatures and grease don't NEED to move, they can choose to stay put and not have to make acrobatics checks.

Also, a prone creature could crawl 5ft to escape the grease. Here are the rules for crawling:

Crawling

You can crawl 5 feet as a move action. Crawling incurs attacks of opportunity from any attackers who threaten you at any point of your crawl. A crawling character is considered prone and must take a move action to stand up, provoking an attack of opportunity.

Moreover, fast creatures may even opt to JUMP OVER the grease. This requires 10 feet of movement for a "running start" and achieving a DC10 acrobatics check (same as not falling so seemingly not a better option) ... if the creature has exceptional movement, jumping over would avoid the half-movement penalty incurred by walking through the grease.

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What do you think?