You have a card in hand with kicker or multikicker.
({3} magic symbol) ({G} magic symbol) , plus enough mana to cast the kicker spell kicked available.
Steps
Activate Phyrexian Devourer by paying ({0} magic symbol) , exling the top card of your library and putting a number of +1/+1 counters on Phyrexian Devourer equal to that card's mana value.
If Phyrexian Devourer's power becomes seven or greater this way, it triggers.
Holding priority, repeat from step 1 until you have an empty library.
With the Phyrexian Devourer triggers on the stack, cast Slippery Bogbonder by paying ({3} magic symbol) ({G} magic symbol) .
When Slippery Bogbonder enters the battlefield, it triggers, moving all +1/+1 counters from Phyrexian Devourer onto Hallar.
Resolve all Phyrexian Devourer triggers from step 2, causing you to sacrifice it.
Cast any kicker or multikicker spell with kicker by paying its mana cost plus its kicker cost.
Hallar triggers, putting a +1/+1 counter on itself, then dealing damage equal to the number of +1/+1 counters on it to each opponent.