Mistform Sliver

Most type-changing creatures rewrite only their own line; this one hands that power to the entire Sliver hivemind. In a deck built on shared abilities, granting "become any creature type" to every Sliver you control turns each of them into an on-demand tribal chameleon, able to suddenly count as Goblins, Elves, or whatever narrow synergy you want to plug into. The crucial limit lives in the wording: the chosen type is gained in addition to its other types, so a Sliver stays a Sliver. This is not an escape hatch from an Engineered Plague or a Sliver-naming sweeper; it adds an identity, it never sheds one. The activated cost is paid per permanent, which makes it a reactive tool rather than an engine. The design folds the Mistform mechanic (creatures that masquerade as other types) into the Sliver framework, where the masquerade propagates across the whole board instead of one body. The honest catch is that type-shifting in a vacuum is mostly a parlor trick: it enables type-specific synergies, and little else. What earns it a slot is the reach: a single 1/1 retrofits an entire army's secondary identity for a turn, the kind of board-wide reach only Sliver telepathy makes possible.