The Goblin Sparring Grounds enters tapped.
{T}: Add {B} or {R}. If this mana is spent to cast a Goblin spell, you get an experience counter.
{B}{R}: Until end of turn, The Goblin Sparring Grounds becomes a Goblin creature in addition to its other types and gains "This creature's power and toughness are each equal to the number of experience counters you have."
The Goblin Sparring Grounds can be your commander.
Legalities
tlrnot legal
duelnot legal
brawlnot legal
pennynot legal
PreDHnot legal
futurenot legal
legacynot legal
modernnot legal
paupernot legal
alchemynot legal
pioneernot legal
vintagenot legal
historicnot legal
standardnot legal
Timelessnot legal
commandernot legal
Gladiatornot legal
Old Schoolnot legal
Premodernnot legal
Oathbreakernot legal
Standard Brawlnot legal
Pauper Commandernot legal
Context
Card type: Legendary Land. Color identity: black/red.