Based on the latest market prices tracked on TCG Stacked, Pikachu is worth about $3.99 USD
This creature gains a number of benefits based on how many times the Ring has tempted you with the benefits maxing out at four instances of Ring tempting
The chance is only very slightly higher than normal and still under 50%

The rest of the Special Illustration Rares and full arts currently rank as follows: Morpeko ex (SIR) : 7,480 yen ($48) Mega Zeraora ex (SIR) : 6,980 yen ($44) Mega Chandelure ex (SIR) : 4,780 yen ($30) Misty's Energy (FA) : 4,280 yen ($27) Gwynn (FA) : 3,980 yen ($25) Gladion's Fighting Spirit (SIR) : 2,480 yen ($16) Mega Darkrai ex (FA) : 2,180 yen ($14) Mega Excadrill ex (FA) : 1,080 yen ($7) Mega Chandelure ex (FA) : 880 yen ($6) Mega Zeraora ex (FA) : 780 yen ($5) Morpeko ex (FA) : 680 yen ($4) Gladion's Fighting Spirit (FA) : 680 yen ($4) Rust Syndicate Grunt (FA) : 680 yen ($4) Lurantis ex (FA) : 580 yen ($4) Wailord ex (FA) : 580 yen ($4) Rampardos ex (FA) : 580 yen ($4) Energy Switch (FA) : 420 yen ($3) Crushing Hammer (FA) : 420 yen ($3) Dark Bell (FA) : 420 yen ($3) Iron Defender (FA) : 280 yen ($2) Heroic Bomb (FA) : 280 yen ($2) Brave Bangle (FA): 280 yen ($2) Slowbro is the top ranked Illustration Rare at 2,500 yen ($16), costing more than double the rest

Look at those colors
Getting to make that play for only one mana and cast multiple spells on the same turn can be backbreaking for the opponent