Poorly Built Contraption

Whenever a goblin enters the battlefield, put an Explosive Counter on this card, then flip a coin. If the result is heads, deal damage to target opponent equal to the number of charge counters on this card. If the result is tails, you take damage equal to the number of charge counters on this card.
{r}{r}{r}: Destroy this card. Goblins you control get +1+1 and gain haste until end of turn.