Here's a list of my ideas thus far:

• This stone gives 1 extra score (i.e. it gives 2 score instead of 1, this is increased to 3 for the square of the prime, 4 for the cube of the prime, etc.)
• When this stone is played, all adjacent stones become neutral (i.e. they don't give score and cannot be played on by either side. Background of a neutral stone is grey)
• When this stone is played, all adjacent stones become communal (they give 1 score to both sides and can be played on by both sides. Background of a communal stone is probably a greyscale gradient)
• Fires adjacent to this stone do not expire
• This stone disappears after three of your turns. On the turn where it disappears, it gives you back the energy used to play it (so you get extra energy for that turn)
• Add a copy of this stone to your deck
• Swap two adjacent tiles anywhere on the board
• Stones can be placed diagonal to this stone
• Stones can be placed two tiles away from this stone
• Place three neutral stones anywhere on the board
• Any empty spaces within a 13-tile diamond (the same shape that a 121 fills with frozen copies) of this stone count as score for you (they only count if they're still empty)
• The number of the next stone played is increased by 1 (that 1 is replaced based on the extra factors added to this stone (like how 13's cost addition works), so if this prime is "p", then a 6p stone adds 6 to the next stone)
• The number of the next stone played is multiplied by 2 after it's played (this 2 is actually 1 + number/this prime, so if this prime is p, then a 2p stone would multiply the next stone by 3, a 3p stone would multiply the next stone by 4, a 4p stone would multiply the next stone by 5, and so on)
• The number of the next stone played is squared after it's played ("after it's played" means that this doesn't affect the energy cost, just the effect)
• Your energy cap is increased by 10 while this stone is on the board

• Multiply two stones in your hand together.
• Cannot be discarded.
• Cannot be placed.
• Can be placed on holes outside the board.
• Remove one space on the board in the same row or column.
• Siphon your opponent's energy.
• A: Equals the average of all cards in hand.
• Swap the effects of two primes (You must have both of these primes in your deck or hand) for the remainder of this battle.
• Tiles on opposite sides of this stone are considered adjacent.
• Can be taken off of the board and placed back in your hand.

101:  The next stone played uses both diagonal and horizontal adjacencies

• Multiply a stone (in this row or column) by 7.

179: Double this stone's value without affecting its energy cost and add one

359: Double this stone's value without affecting its energy cost and add one

719: Double this stone's value without affecting its energy cost and add one

1439: Double this stone's value without affecting its energy cost and add one

2879: If you have less than 4 stones on the board, win immediately