it only deals 20 according to the card?
and to fix the cards chain reaction problem say: cannot be targeted by spells, only explodes when killed by a creatures attack, things along those lines
for the chain reaction, by the rules set now, only 1 creature can have gravity force on them so for coding reasons have it say only may play 1 red giant at a time, or have the gravity force switch around like it would in the game (ie you have 2 armagios, you use ability on one, almost dies, activate other amagio, only for this card, that switch happens when you play a new red giant)
If it has 30, there is virtually no way to set off all of them at once, especially if only one of them can have gravity pull on them (AI won't target the other cards if one is closer to death, and human players would be stupid enough to kill 6 of these on purpose)
as for the frequency of attacks, most deck will have some kind of muscle on them, so 1 turn of a dragons attack can take about the same amount off as 10 turns of poison, so if you do 30 hp, it will go in 3 turns with just that
Yellow text: There's probably another way to reword this card, but for now, adding those lines will mean that he'll probably have several lines of description text that can't fit into the card box, which is poor formatting. The suggestion of the poison is to accommodate for the small space the card author has. With that said, the chain reaction 'problem' is fixed when it's killed by poison, and in my opinion, the description is concise enough that it works.
Orange text: That's another possible solution if the creature is killed when afflicted with Gravity Pull, but that implies that the opponent has sufficient creatures to deal that much damage, and also feels a little... weird. How are creatures able to directly attack a Red Giant/Sun? O_o I suppose this idea could be more practical and useful in the long run though.
This would defenently be OP if you had a mirror shield.
Problem - the red text below implies that reflective shields
cannot prevent this damage.
...
[snip]
The idea is a weird combo between Unstable Gas (which is BAD if you play this and the opponent has an Jade/Mirror Shield in hand, meaning that you're going to take the damage)
I guess the damage won´t be reflected as it´s a creature and not a spell.