Lifelink

Modular 1 (This creature enters with a +1/+1 counter on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Offspring (You may pay an additional as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)

At the beginning of combat on your turn, target Mouse you control gains your choice of double strike or trample until end of turn.

The second spell you cast each turn costs less to cast.

Celebration — At the beginning of combat on your turn, if two or more nonland permanents entered the battlefield under your control this turn, target creature you control gets +1/+1 until end of turn.

Valiant — Whenever Veteran Guardmouse becomes the target of a spell or ability you control for the first time each turn, it gets +1/+0 and gains first strike until end of turn. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)