Where is this grappling rule?

[kengar]

WOTC had a feature on their site a while back called "Gamestoppers." For those of you who might not have seen it, the column addressed a different "Special rule" each installment. In one column they discussed the Grappling rules. The example used was a party fighting an Otyugh. The following is a quote from the column:

...You take 11 points of damage, and since it's got the improved grab ability, it can automatically try to grapple you. You and the otyugh need to make opposed grapple checks. The otyugh has a base attack of +9, a Strength modifier of +4, and a size modifier for being Huge of +8, for a total of +21. Luckily for you, it doesn't want to focus all its concentration on grappling you, what with all the other yummy looking targets in reach, so it tries to grapple you using only its tentacle and suffers a -20 penalty to the roll. (emphasis mine)

Where is this rule about -20 to grapple for "splitting attention"?

 

[hong]

See the MM description of improved grab, p.9.

 

[Galfridus]

I believe it's in the beginning of the Monster Manual, and it definitely shows up in Monster Manual II.

 

[kengar]

Thanks much!