Definitely trapped and bleed as above says, however I disagree with RasAlgethi24 on BoP. Powerful is awful imho; much better to go with miranae if CDR isn't an issue (Gogok is great if CDR is an issue).
Reasoning: the proc on powerful is unreliable and void if you have a death/run back (and highly reliant on elite pack density). Miranae is consistent. Also Rift Guardian kill times can be rough with stampede and I've found that the single target damage of miranae outweighs the 15% ED on BoP especially when taking into account the proc on BoP falling off during the RG kill.
So: Miranae outperforms BoP in both phases of Grifts.