FEH - Riev GHB with big brain L1 Lex

Riev's tome debuffs all allies within a 2-square range of the slowest unit, so a workaround for tank users is to bring someone who under-speeds the slowest tank and keep them away from combat units. Units with long range buffing effects like Mila and Gatekeeper should also work pretty well, so are Opening/Gap skills, possibly.