A few years ago, I edited the ROM to make Tiga killable. As far as I know, I was the first person to ever defeat him. Of course the game isn't programmed to allow you to win that fight, so when he dies the game continues as if he beat you. There's no real reason to kill him apart from bragging rights.
Tiga is impossible to beat in normal gameplay. It took me ages to figure out why. My initial theory was that the game considered any HP between 0 and -998 to be dead, and Tiga's HP was -999 or below, so the only way to kill him would be to heal him. Of course the first time I edited the ROM I discovered this was not the case.
ShinryuuX's enemy list is accurate on Tiga's stats--he does have 65,535 HP. But when you deal 70,000 damage to him, he doesn't die. I spent hours trying to figure out if there was a byte somewhere in his stats that made him unkillable. It turns out it's just the way the game handles high numbers.
The highest actual HP that ever appears in the game is Deathevn's at 10,000, so the game can obviously handle numbers that high. In fact, I think the game can count perfectly reasonably up to 32,767, but it considers the number 32,768 to be infinite, and most of the numbers after that are treated as if they were much smaller, up to 65,535, which is again infinite. I haven't checked all these numbers individually, but I believe this is true from what I have checked.
What's interesting is that if you just make Tiga's HP one point lower--65,534--he goes from being impossible to kill to being a one hit kill.
So you can defeat Tiga by setting his HP to any number under 32,768. Here are two Game Genie codes for people who want to beat him.
First, the easy code for those who just want to watch him die. This will set his HP to 256, so it should only take a few hits to kill him. DDC0-D499
Now the hard code for those who want Tiga to be a challenge. This sets his HP to 32,767, which I think is as high as it can possibly go--more than three times that of the final boss of the game. EEC0-D4F9 5EC0-D499
I've tested these on the retranslated ROM. I think they'll work on other versions of the game. Please try them out and let me know. --- Member of SEM Read my religious/philosophical views on the Philosophy board. Link in quote.