If youre playing cheap spells like Shelter or Take Up Shield, casting multiple spells per turn is easily achievable and will give Arcee a bunch of counters
If this face-up card in its owner's control leaves the field because of an opponent's card effect: You can Special Summon 2 "Krawler" monsters with different names from your Deck in face-down Defense Position, except "Krawler Glial"

Academic Probation Arachnus Web Archon of the Triumvirate Arrest Avacyn's Collar, the Symbol of Her Church (playtest) Azorius Arrester Azorius Justiciar Bound in Gold Braided Net Clarion Conqueror Collector Ouphe Cursed Totem Damping Matrix Deadlock Trap Demotion Desert's Hold Detainment Spell Detention Vortex Disruptor Flute Dovin Baan Drana and Linvala Edifice of Authority Encrust Faith's Fetters Gelid Shackles Gobsmacked Hold for Questioning Ice Cage Inaction Injunction Intercessor's Arrest Interdict Isperia's Skywatch Karn, the Great Creator Katabatic Winds Koma, Cosmos Serpent Koma, Cosmos Serpent Krasis Incubation Lavinia of the Tenth Lawmage's Binding Linvala, Keeper of Silence Linvala, Shield of Sea Gate Lost in Thought Lyev Decree Lyev Skyknight Martial Law Mythos of Vadrok Nahiri's Binding New Prahv Guildmage Null Rod One Thousand Lashes Petrified Hamlet Petrify Phyrexian Revoker Pithing Needle Planar Disruption Prison Sentence Prison Term Realmbreaker's Grasp Scheming Fence Seatower Imprisonment Secure Detention Serra Bestiary Sharkey, Tyrant of the Shire Sorcerous Spyglass Soulsworn Spirit Stasis Cocoon Stony Silence Stormcage Containment Facility Stuck in Summoner's Sanctum Stupefying Touch Suppression Bonds Tax Collector

though best to err on the side of caution
It doesnt have the same ceiling, but it triggers off opposing creatures dying, which results in a higher floor