Name:Battlefield Scavenger
ManaCost:1 R
Types:Creature Jackal Rogue
PT:2/2
K:You may exert CARDNAME as it attacks.
T:Mode$ Exerted | ValidCard$ Creature.YouCtrl | TriggerZones$ Battlefield | Execute$ TrigDiscard | TriggerDescription$ Whenever you exert a creature, you may discard a card. If you do, draw a card.
// This code presumes that you are only ever allowed to exert creatures you control. If this is changed in the future, it will need an update.
SVar:TrigDiscard:AB$ Discard | Cost$ 0 | Defined$ You | NumCards$ 1 | Mode$ TgtChoose | RememberDiscarded$ True | Optional$ True | SubAbility$ DBDraw

SVar:DBDraw:DB$ Draw | NumCards$ 1 | ConditionDefined$ Remembered | ConditionPresent$ Card | ConditionCompare$ GE1 | SubAbility$ DBCleanup

SVar:DBCleanup:DB$ Cleanup | ClearRemembered$ True 
Oracle:You may exert Battlefield Scavenger as it attacks. (It won't untap during your next untap step.)\nWhenever you exert a creature, you may discard a card. If you do, draw a card.