Cheapest priced copy (Outlaws of Thunder Junction): $0.49 at Card Kingdom, near mint, their price list as of .
Kellan Joins Up 
Legendary Enchantment · Rare · Outlaws of Thunder Junction · #354
When Kellan Joins Up enters, you may exile a nonland card with mana value 3 or less from your hand. If you do, it becomes plotted. (You may cast it as a sorcery on a later turn without paying its mana cost.)
Whenever a legendary creature you control enters, put a +1/+1 counter on each creature you control.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
4 printings · $0.49 to $1.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Outlaws of Thunder Junction | 212 | Rare | $0.49 | $0.49 |
| Outlaws of Thunder Junction | 354 | Rare | $0.49 | $0.99 |
| Outlaws of Thunder Junction Promos | 212p | Rare | $0.49 | $0.49 |
| Outlaws of Thunder Junction Promos | 212s | Rare | — | $1.79 |
10 rulings from Wizards of the Coast
- 12 April 2024If a card doesn't have a mana cost, its mana value is 0.
- 12 April 2024If the mana cost of a card in your hand includes {X}, X is 0 for the purpose of determining its mana value.
- 12 April 2024Exiling a card using its plot ability is a special action. Once you announce you're taking that action, no other player can respond by trying to remove that card from your hand.
- 12 April 2024You can't cast a plotted card on the same turn it became plotted. On any future turn, you may cast that card from exile without paying its mana cost during your main phase while the stack is empty.
- 12 April 2024The mana value of a split card in your hand is based on the combined mana cost of its two halves.
- 12 April 2024Plot abilities are written "Plot [cost]," which means "Any time you have priority during your main phase while the stack is empty, you may pay [cost] and exile this card from your hand. It becomes plotted."
- 12 April 2024If you're casting a plotted card from exile without paying its mana cost, you can't choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the plotted card has any mandatory additional costs, those must still be paid to cast the spell.
- 12 April 2024If a plotted card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 12 April 2024If multiple legendary creatures enter the battlefield under your control at the same time, Kellan Joins Up's last ability will trigger once for each of those creatures.
- 7 June 2024If an instant or a card with flash is plotted this way, you can still cast it only when you have priority during your main phase while the stack is empty.