Nexus Factory

[Superman]

Nexus Factory
Land

Tap: Add one colorless mana to your mana pool.
Tap: Target creature gets +1/+1 until the end of turn.

[Matt]

Reminds me of Pendlehaven. Can you imagine getting multiples of these into play?

[Jacob Orlove]

The most recent version is Okina, Temple to the Grandfathers, which shows that your version is almost certainly undercosted.

[Superman]

Yeah but Grandfather adds Green.

[Nibble]

It also can only target legendary creatures, and is legendary itself. It has way more drawbacks to just be solved by making the mana colorless.

[Ephraim]

It is more relevant to note that they have only ever printed one land that gives creatures +n/+n that didn't have some targetting restriction ([card]Heart of Yavimaya[/card], which requires you to sacrifice a forest to play it). [card]Pendelhaven[/card] only helped 1/1 creatures, [card]Griffin Canyon[/card] and [card]Daru Encampment[/card] were limited by creature type. [card]Blinkmoth Nexus[/card] and [card]Mishras Factory[/card] only help out their own kind. This is going to need some sort of penalty. Either give it a targetting restriction of some sort or an activation cost (no less than .)

[Superman]

How about

Nexus Factory
Land

Tap: Add one colorless mana to your mana pool.
Tap: Target creature gets +1/+1 until the end of turn Nexus Factory doesn't untap during your next untap step unless you pay 1.

[Ephraim]

Maybe if you took out the "unless" clause. That just makes it feel as though you're paying {1} to activate this, which isn't enough. If it just said "{T}: Target creature gets +1/+1 until end of turn. Nexus Factory doesn't untap during your next untap step." That would probably be fine.

I'm sure you're aware that the name also will need to be changed. "Field of Champions" is a decent name.