you cast Mul daya Channelers and the card on top is a creature. can someone cast a lightning bolt targeting the Channelers and killing it before the +3+3 takes effect? or does the effect take place as soon as it enters the battlefield?
If I'm not mistaken, the Channelers have three static abilities. This means that they are always in effect as soon as it is on the battlefield. So, no, Lightning Bolt won't help unless the top card of your library is a land.
You are not mistaken, Crono. No "When" "Whenever" or "At" means it isn't triggered, no COST : EFFECT means it isn't activated, and no "If" means it isn't a replacement ability. That leaves us with static, meaning it doesn't turn on, it's ALWAYS on.
The effect takes place as soon as it enters the battlefield. The moment it is on the battlefield and is a legal target for a Lightning Bolt, the first static ability is already revealing the top card of your library. As long as that card is a creature, your Channelers are 5/5, and will not die. Do note, however, if you were to draw a card, or shuffle, or in any way have the top card of your land NOT be a creature during that same turn, it will die because it will revert to a 3/3, marked with 3 damage, so SBAs will kill it.
The effect takes place as soon as it enters the battlefield. The moment it is on the battlefield and is a legal target for a Lightning Bolt, the first static ability is already revealing the top card of your library. As long as that card is a creature, your Channelers are 5/5, and will not die. Do note, however, if you were to draw a card, or shuffle, or in any way have the top card of your land NOT be a creature during that same turn, it will die because it will revert to a 3/3, marked with 3 damage, so SBAs will kill it.
The latest Comprehensive Rules are also good, and can be found here.