Pax said:
The comparison is: "how dangerous is/are the square(s) tumbled through" or "how complex and difficult is the spell being cast". Concentration is scalar to the difficulty of what you are doing, and that difficulty increases as you rise in level.
Tumble doesn't. Yet it should.
Tumble scales to the difficulty of what you are doing: those modifiers I was talking about on the first page of this thread.
How about this. It is a Concentration DC of 16 to cast
Magic Missile when you are standing right next to the Inkeeper's son. It is a Concentration DC of 16 to cast
Magic Missile when you are standing next to the Huge Hulking Beast.
I don't for the life of me know
why a wizard would want to be next to the Huge Hulking Beast when he casts that spell, but that's when you would cast defensively: when you would otherwise provoke a melee AoO.
If the wizard rolls a successful Concentration check of 16, no matter his level or the foe's level (not considering the feat), then the wizard will never incur an attack of opportunity for casting a first level spell next to a foe. The DC raises if he wants to cast a higher level spell: a 9th level spell concentration DC is 24.
The base DC for tumbling around one opponent is 15. No matter the tumbler or the foe, if a 15 is made, the tumbler will never incur an AoO. If he wants to tumble past two, the DC gets harder by +2, but we already know that. Here's what's fun: tumbling through Billy the Inkeeper's occupied square has a harder DC than the wizard casting Power Word: Kill right next to the Huge Hulking Monster.
So, Pax, tell me how Tumble is so unlike Concentration that it breaks the game.
And allow me to pre-empt you on Spellcasting Harrier; I believe that Feat is not in the Core rulebooks. I am sure if you looked you would find a similar feat that would allow you to make tumble checks harder when opponents try to tumble past you by granting you an AoO.