If I have Faeburrow Elder and any Red creature but no untaped Red source and I begin to cast Heartfire and sacrifice the Red creature before tapping the elder for mana will the game back up?
While casting Heartfire, if that spell's "total cost includes a mana payment" as it normally does, you activate mana abilities (such as Faeburrow Elder's last ability) before you pay the spell's costs, including sacrificing a creature or planeswalker (C.R. 608.2f, 608.2h). Note that Faeburrow Elder's last ability doesn't care whether permanents you control are tapped or untapped.
Thus, if you tap Faeburrow Elder for mana while casting Heartfire, you add R if you control a red creature, even if you will then sacrifice that creature to pay for Heartfire.
This isn't an issue of the order in which you pay costs. This is an issue of how mana abilities work when paying costs. As peteroupc said, you must activate mana abilities *before* paying any costs. So, you would activate the Elder prior to being able to either pay mana or sacrifice a creature. So you will have the red mana you need.
You can choose what order to pay costs in, so if you pay the sacrifice cost before the mana cost, you are no longer able to pay for mana wise.
No, that's not how it works. You activate mana abilities before you pay the cost of a spell with mana in its cost (C.R. 601.2f). In general, to pay for Heartfire, you—
spend 1R, which is Heartfire's mana cost (C.R. 118.3a, 601.2f), and
Okay I got a question and i hope i get some help with this. I am running faeburrow Elder in a 3 color deck and i also have perplexing chimera, so I tend to take other people's creatures or enchantments, ect. So my question is would I be able to use other cards abilities with the elder and do I also gain a +1/+1 for them? I know the max amount is +5/+5 among color permanent I color. So technically I gain control of the card. Some people tell me I can only have 3 counters on it cause I'm only running a 3 color deck.
If you take control of a permanent with a color outside the scope of your deck, well, then you now have an additional color to count among the permanents you control. This is true even in a Commander game. Cards don't lose colors just because their controller changes. Also, hybrid cards count for all of their colors, even if you your deck plays them for only one color.
The Elder has nothing to do with counters, it just gets a continuously updated buff based on colors among the permanents you control, which can range from 0 to 5 (but is usually at least 2, since the Elder is usually w/g). Only if an effect uses the word "counter" are counters involved.
edit:
The Commander rule, that didn't let you produce mana outside your commander's color identity, has been abolished quite some time ago. Now you can produce mana of any of the 5 colors regardless of your deck's colors.
Thus, if you tap Faeburrow Elder for mana while casting Heartfire, you add R if you control a red creature, even if you will then sacrifice that creature to pay for Heartfire.
The Elder has nothing to do with counters, it just gets a continuously updated buff based on colors among the permanents you control, which can range from 0 to 5 (but is usually at least 2, since the Elder is usually w/g). Only if an effect uses the word "counter" are counters involved.
edit:
The Commander rule, that didn't let you produce mana outside your commander's color identity, has been abolished quite some time ago. Now you can produce mana of any of the 5 colors regardless of your deck's colors.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
Thus, in a Commander game, that player can generally still—
See also this thread and this thread.
EDIT (May 24, 2020; Oct. 12, 2022): Edited.