what is the best way to make an explosion in the game engine?

Looking at other games is usually a good start. Id say you’d need a couple of things.

  1. A shockwave. Using a shockwave on an alpha texture with a size ipo that spreads from the point of explosion.

  2. The fireball, again flame textures with size ipos or you could use a semi-sphere, depends what look you want.

  3. Shaking camera ipo.

  4. Smoke.

There’s no best way to do it, it depends on what effect you want, then dissecting it into individual components, then deciding how you’re going to achieve them.

EDIT: Assuming from your grenade thread you want an exploding grenade, in which case you wont need the fire ball, instead you could use multiple edit object actuators to add bits of grenade flying in different directions.

when you say a shockwave, do you mean a macromedai director shockwave file?

No, he means like a literal shockwave.