You have a card in hand with kicker or multikicker.
You have enough mana available to cast the kicker spell kicked.
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.
Resolve the first Phyrexian Devourer trigger, causing you to sacrifice it.
When Phyrexian Devourer leaves the battlefield, Resourceful Defense triggers, putting a number of +1/+1 counters on Hallar equal to the number Phyrexian Devourer had.
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.